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  • 1.
    Aguilar, Ximena
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Blomberg, Jeanette
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Brännström, Kristoffer
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Olofsson, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Schleucher, Jurgen
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Björklund, Stefan
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Interaction Studies of the Human and Arabidopsis thaliana Med25-ACID Proteins with the Herpes Simplex Virus VP16-and Plant-Specific Dreb2a Transcription Factors2014Ingår i: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 9, nr 5, s. e98575-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Mediator is an evolutionary conserved multi-protein complex present in all eukaryotes. It functions as a transcriptional coregulator by conveying signals from activators and repressors to the RNA polymerase II transcription machinery. The Arabidopsis thaliana Med25 (aMed25) ACtivation Interaction Domain (ACID) interacts with the Dreb2a activator which is involved in plant stress response pathways, while Human Med25-ACID (hMed25) interacts with the herpes simplex virus VP16 activator. Despite low sequence similarity, hMed25-ACID also interacts with the plant-specific Dreb2a transcriptional activator protein. We have used GST pull-down-, surface plasmon resonance-, isothermal titration calorimetry and NMR chemical shift experiments to characterize interactions between Dreb2a and VP16, with the hMed25 and aMed25-ACIDs. We found that VP16 interacts with aMed25-ACID with similar affinity as with hMed25-ACID and that the binding surface on aMed25-ACID overlaps with the binding site for Dreb2a. We also show that the Dreb2a interaction region in hMed25-ACID overlaps with the earlier reported VP16 binding site. In addition, we show that hMed25-ACID/Dreb2a and aMed25-ACID/Dreb2a display similar binding affinities but different binding energetics. Our results therefore indicate that interaction between transcriptional regulators and their target proteins in Mediator are less dependent on the primary sequences in the interaction domains but that these domains fold into similar structures upon interaction.

  • 2. Balciunas, Darius
    et al.
    Hallberg, Magnus
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Björklund, Stefan
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Ronne, Hans
    Functional interactions within yeast mediator and evidence of differential subunit modifications2003Ingår i: Journal of Biological Chemistry, ISSN 0021-9258, E-ISSN 1083-351X, Vol. 278, nr 6, s. 3831-3839Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    It is possible to recruit RNA polymerase II to a target promoter and, thus, activate transcription by fusing Mediator subunits to a DNA binding domain. To investigate functional interactions within Mediator, we have tested such fusions of the lexA DNA binding domain to Med1, Med2, Gal11, Srb7, and Srb10 in wild type, med1, med2, gal11, sin4, srb8, srb10, and srb11 strains. We found that lexA-Med2 and lexA-Gal11 are strong activators that are independent of all Mediator subunits tested. lexA-Srb10 is a weak activator that depends on Srb8 and Srb11. lexA-Med1 and lexA-Srb7 are both cryptic activators that become active in the absence of Srb8, Srb10, Srb11, or Sin4. An unexpected finding was that lexA-VP16 differs from Gal4-VP16 in that it is independent of the activator binding Mediator module. Both lexA-Med1 and lexA-Srb7 are stably associated with Med4 and Med8, which suggests that they are incorporated into Mediator. Med4 and Med8 exist in two mobility forms that differ in their association with lexA-Med1 and lexA-Srb7. Within purified Mediator, Med4 is present as a phosphorylated lower mobility form. Taken together, these results suggest that assembly of Mediator is a multistep process that involves conversion of both Med4 and Med8 to their low mobility forms.

  • 3.
    Björklund, Stefan
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Gustafsson, Claes M
    The mediator complex.2004Ingår i: Advances in Protein Chemistry, ISSN 0065-3233, E-ISSN 1557-8941, Vol. 67, s. 43-65Artikel i tidskrift (Refereegranskat)
  • 4.
    Björklund, Stefan
    et al.
    Umeå universitet, Medicinsk fakultet, Medicinsk kemi och biofysik.
    Gustafsson, Claes M
    The yeast Mediator complex and its regulation.2005Ingår i: Trends in Biochemical Sciences, ISSN 0968-0004, Vol. 30, nr 5, s. 240-4Artikel i tidskrift (Refereegranskat)
  • 5.
    Björklund, Stefan
    et al.
    Umeå universitet, Medicinsk fakultet, Medicinsk kemi och biofysik.
    Hjortsberg, K
    Johansson, Erik
    Umeå universitet, Medicinsk fakultet, Medicinsk kemi och biofysik.
    Thelander, Lars
    Umeå universitet, Medicinsk fakultet, Medicinsk kemi och biofysik.
    Structure and promoter characterization of the gene encoding the large subunit (R1 protein) of mouse ribonucleotide reductase.1993Ingår i: Proceedings of the National Academy of Science U S A, ISSN 0027-8424, Vol. 90, nr 23, s. 11322-6Artikel i tidskrift (Refereegranskat)
  • 6. Björklund, Stefan
    et al.
    Kim, Y J
    Mediator of transcriptional regulation.1996Ingår i: TIBS -Trends in Biochemical Sciences. Regular ed., ISSN 0968-0004, E-ISSN 1362-4326, Vol. 21, nr 9, s. 335-7Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A multi-protein complex, termed mediator, has been isolated from yeast, based on its requirement for transcriptional activation in a system reconstituted from pure RNA polymerase II and general transcription factors. Mediator polypeptides include the products of many genes previously recovered from screens for mutations affecting transcription. This connection between biochemical and genetic studies reveals that mediator is important for both activation and repression of transcription, and that mediator plays a role in transcriptional regulation in vivo as well as in vitro. Mediator binds the carboxy-terminal domain of RNA polymerase II, forming a polymerase holoenzyme, whose possible association with additional proteins is a subject of some controversy.

  • 7.
    Björklund, Stefan
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Skog, Sven
    Tribukait, Bernard
    Thelander, Lars
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    S-phase-specific expression of mammalian ribonucleotide reductase R1 and R2 subunit mRNAs1990Ingår i: Biochemistry, ISSN 0006-2960, E-ISSN 1520-4995, Vol. 29, nr 23, s. 5452-5458Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Ribonucleotide reductase in mammalian cells is composed of two nonidentical subunits, proteins R1 and R2, each inactive alone. The R1 protein is present in excess in proliferating cells, and its levels are constant during the cell cycle. Expression of the R2 protein, which is limiting for enzyme activity, is strictly S-phase-correlated. In this paper, we have used antisense RNA probes in a solution hybridization assay to measure the levels of R1 and R2 mRNA during the cell cycle in centrifugally elutriated cells and in cells synchronized by isoleucine or serum starvation. The levels of both transcripts were very low or undetectable in G0/G1-phase cells, showed a pronounced increase as cells progressed into S phase, and then declined when cells progressed into G2 + M phase. The R1 and R2 transcripts increased in parallel, starting slightly before the rise in S-phase cells, and reached the same levels. The relative lack of cell cycle dependent variation in R1 protein levels, obtained previously, may therefore simply be a consequence of the long half-life of the R1 protein. Hydroxyurea-resistant, R2-overproducing mouse TA3 cells showed the same regulation of the R1 and R2 transcripts as the parental cells, but with R2 mRNA at a 40-fold higher level.

  • 8.
    Björklund, Stefan
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Skogman, E
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Thelander, Lars
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    An S-phase specific release from a transcriptional block regulates the expression of mouse ribonucleotide reductase R2 subunit1992Ingår i: EMBO Journal, ISSN 0261-4189, E-ISSN 1460-2075, Vol. 11, nr 13, s. 4953-4959Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Ribonucleotide reductase (RR) activity in mammalian cells is closely linked to DNA synthesis. The RR enzyme is composed of two non-identical subunits, proteins R1 and R2. Both proteins are required for holoenzyme activity, which is regulated by S-phase specific de novo synthesis and breakdown of the R2 subunit. In quiescent cells stimulated to proliferate and in elutriated cell populations enriched in the various cell cycle phases the R2 protein levels are correlated to R2 mRNA levels that are low in G0/G1-phase cells but increase dramatically at the G1/S border. Using an R2 promoter-luciferase reporter gene construct we demonstrate an unexpected early activation of the R2 promoter as cells pass from quiescence to proliferation. However, due to a transcriptional block, this promoter activation only results in very short R2 transcripts until cells enter the S-phase, when full-length R2 transcripts start to appear. The position for the transcriptional block was localized to a nucleotide sequence approximately 87 bp downstream from the first exon/intron boundary by S1 nuclease mapping of R2 transcripts from modified in vitro nuclear run-on experiments. These results identify blocking of transcription as a mechanism to control cell cycle regulated gene expression.

  • 9.
    Blomberg, Jeanette
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Aguilar, Ximena
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Brännström, Kristoffer
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Rautio, Linn
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Olofsson, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Wittung-Stafshede, Pernilla
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Björklund, Stefan
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Interactions between DNA, transcriptional regulator Dreb2a and the Med25 mediator subunit from Arabidopsis thaliana involve conformational changes2012Ingår i: Nucleic Acids Research, ISSN 0305-1048, E-ISSN 1362-4962, Vol. 40, nr 13, s. 5938-5950Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Mediator is a multiprotein coregulatory complex that conveys signals from DNA-bound transcriptional regulators to the RNA polymerase II transcription machinery in eukaryotes. The molecular mechanisms for how these signals are transmitted are still elusive. By using purified transcription factor Dreb2a, mediator subunit Med25 from Arabidopsis thaliana, and a combination of biochemical and biophysical methods, we show that binding of Dreb2a to its canonical DNA sequence leads to an increase in secondary structure of the transcription factor. Similarly, interaction between the Dreb2a and Med25 in the absence of DNA results in conformational changes. However, the presence of the canonical Dreb2a DNA-binding site reduces the affinity between Dreb2a and Med25. We conclude that transcription regulation is facilitated by small but distinct changes in energetic and structural parameters of the involved proteins.

  • 10. Bourbon, Henri-Marc
    et al.
    Aguilera, Andres
    Ansari, Aseem Z
    Asturias, Francisco J
    Berk, Arnold J
    Björklund, Stefan
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Blackwell, T Keith
    Borggrefe, Tilman
    Carey, Michael
    Carlson, Marian
    Conaway, Joan W
    Conaway, Ronald C
    Emmons, Scott W
    Fondell, Joseph D
    Freedman, Leonard P
    Fukasawa, Toshio
    Gustafsson, Claes M
    Han, Min
    He, Xi
    Herman, Paul K
    Hinnebusch, Alan G
    Holmberg, Steen
    Holstege, Frank C
    Jaehning, Judith A
    Kim, Young-Joon
    Kuras, Laurent
    Leutz, Achim
    Lis, John T
    Meisterernest, Michael
    Naar, Anders M
    Nasmyth, Kim
    Parvin, Jeffrey D
    Ptashne, Mark
    Reinberg, Danny
    Ronne, Hans
    Sadowski, Ivan
    Sakurai, Hiroshi
    Sipiczki, Matthias
    Sternberg, Paul W
    Stillman, David J
    Strich, Randy
    Struhl, Kevin
    Svejstrup, Jasper Q
    Tuck, Simon
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Umeå centrum för molekylär patogenes (UCMP).
    Winston, Fred
    Roeder, Robert G
    Kornberg, Roger D
    A unified nomenclature for protein subunits of mediator complexes linking transcriptional regulators to RNA polymerase II.2004Ingår i: Molecular Cell, ISSN 1097-2765, Vol. 14, nr 5, s. 553-7Artikel i tidskrift (Refereegranskat)
  • 11. Broach, James R
    et al.
    Bharatula, Vasudha
    Chereji, Razvan
    Elfving, Nils
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Björklund, Stefan
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Morozov, Alexandre
    The Msn2 mediated stress response: Survival based on "hedging your bet" and a dynamic interplay of transcription factor binding and nucleosome occupancy2015Ingår i: Yeast, ISSN 0749-503X, E-ISSN 1097-0061, Vol. 32, nr Suppl. 1, s. S221-S222Artikel i tidskrift (Övrigt vetenskapligt)
    Abstract [en]

    Yeast cell subjected to many different stresses elicit an acute transcriptional stress response mediated by the Msn2 transcription factor, which alters expression of both a stress specific-cohort of genes as well as a common cohort of genes that changes expression in a stereotypic fashion upon exposure to any of a wide variety of stresses. We have shown by dynamic single cell analysis that stresses regulate Msn2 activity through cytoplasm to nuclear relocalization but do so in an unusual way: stresses induce increased frequency of bursts of short-lived, recurrent periods of Msn2 nuclear localization with different stresses eliciting different patterns of bursts. Moreover, genetically identical cells subject to an identical stress can behave quite differently, with some cells mounting a robust nuclear occupancy of Msn2 while others show no nuclear localization at all. We have proposed that this idiosyncratic behavior allows populations of cells to “hedge their bet” as to what will be the optimum strategy for surviving the ensuing stress. We have used computational modeling and single cell analysis to determine that bursting is a consequence of noise in the stress signaling pathways amplified by the small number of Msn2 molecules in the cell. Moreover, we have applied genome wide chromatin immunoprecipitation and nucleosome profiling to address how different stresses determine where Msn2 binds under a particular stressful conditions, and thus what genes are regulated by that stress, and how that binding affects, and is affected by, nucleosome positioning and other transcription factor binding. These results provide in vivo validation of Widon's model of indirect cooperativity of transcription factor binding, mediated by partial unwinding of nucleosomes by one transcription factor to allow access for a second transcription factor to a previously occluded binding site. Finally, we have addressed the “bet hedging” hypothesis by showing that persistence of the Msn2-mediated stress response yields cell growth arrest and have identified the targets responsible for that growth arrest. We have applied experimental evolution paradigms to address the relative fitness of cells exhibiting stochastic stress responses versus those with a uniform response. In short, our results indicate that the stress response is complex and that complexity is critical for cell survival.

  • 12.
    Bäckström, Stefan
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Elfving, Nils
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Nilsson, Robert
    Wingsle, Gunnar
    Björklund, Stefan
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Purification of a plant mediator from Arabidopsis thaliana identifies PFT1 as the Med25 subunit2007Ingår i: Molecular Cell, ISSN 1097-2765, E-ISSN 1097-4164, Vol. 26, nr 5, s. 717-729Artikel i tidskrift (Refereegranskat)
  • 13.
    Chabes, Anna Lena
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Björklund, Stefan
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Thelander, Lars
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    S phase-specific transcription of the mouse ribonucleotide reductase R2 gene is dependent on an upstream promoter activating region and a proximal repressive E2F binding site.Manuskript (Övrigt vetenskapligt)
  • 14.
    Chabes, Anna Lena
    et al.
    Umeå universitet, Medicinsk fakultet, Medicinsk kemi och biofysik.
    Björklund, Stefan
    Umeå universitet, Medicinsk fakultet, Medicinsk kemi och biofysik.
    Thelander, Lars
    Umeå universitet, Medicinsk fakultet, Medicinsk kemi och biofysik.
    S Phase-specific transcription of the mouse ribonucleotide reductase R2 gene requires both a proximal repressive E2F-binding site and an upstream promoter activating region.2004Ingår i: Journal of biological chemistry, ISSN 0021-9258, Vol. 279, nr 11, s. 10796-807Artikel i tidskrift (Refereegranskat)
  • 15. Chereji, Razvan V.
    et al.
    Bharatula, Vasudha
    Elfving, Nils
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Blomberg, Jeanette
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Larsson, Miriam
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Morozov, Alexandre V.
    Broach, James R.
    Björklund, Stefan
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Mediator binds to boundaries of chromosomal interaction domains and to proteins involved in DNA looping, RNA metabolism, chromatin remodeling, and actin assembly2017Ingår i: Nucleic Acids Research, ISSN 0305-1048, E-ISSN 1362-4962, Vol. 45, nr 15, s. 8806-8821Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Mediator is a multi-unit molecular complex that plays a key role in transferring signals from transcriptional regulators to RNA polymerase II in eukaryotes. We have combined biochemical purification of the Sac-charomyces cerevisiae Mediator from chromatin with chromatin immunoprecipitation in order to reveal Mediator occupancy on DNA genome-wide, and to identify proteins interacting specifically with Mediator on the chromatin template. Tandem mass spectrometry of proteins in immunoprecipitates of mediator complexes revealed specific interactions between Mediator and the RSC, Arp2/Arp3, CPF, CF 1A and Lsm complexes in chromatin. These factors are primarily involved in chromatin remodeling, actin assembly, mRNA 3'-end processing, gene looping and mRNA decay, but they have also been shown to enter the nucleus and participate in Pol II transcription. Moreover, we have found that Mediator, in addition to binding Pol II promoters, occupies chromosomal interacting domain (CID) boundaries and that Mediator in chromatin associates with proteins that have been shown to interact with CID boundaries, such as Sth1, Ssu72 and histone H4. This suggests that Mediator plays a significant role in higher-order genome organization.

  • 16.
    Elfving, Nils
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Chereji, Razvan
    Department of Physics and Astronomy and BioMaPS Institute for Quantitative Biology, Rutgers University.
    Larsson, Miriam
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Morozov, Alexandre
    Department of Physics and Astronomy and BioMaPS Institute for Quantitative Biology, Rutgers University.
    Broach, James
    Department of Molecular Biology, Princeton University.
    Björklund, Stefan
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Mediator exists in multiple forms and is predominantly associated to promoters with low nuclesome densityManuskript (preprint) (Övrigt vetenskapligt)
  • 17.
    Elfving, Nils
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Chereji, Razvan V.
    Bharatula, Vasudha
    Björklund, Stefan
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Morozov, Alexandre V.
    Broach, James R.
    A dynamic interplay of nucleosome and Msn2 binding regulates kinetics of gene activation and repression following stress2014Ingår i: Nucleic Acids Research, ISSN 0305-1048, E-ISSN 1362-4962, Vol. 42, nr 9, s. 5468-5482Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The transcription factor Msn2 mediates a significant proportion of the environmental stress response, in which a common cohort of genes changes expression in a stereotypic fashion upon exposure to any of a wide variety of stresses. We have applied genome-wide chromatin immunoprecipitation and nucleosome profiling to determine where Msn2 binds under stressful conditions and how that binding affects, and is affected by, nucleosome positioning. We concurrently determined the effect of Msn2 activity on gene expression following stress and demonstrated that Msn2 stimulates both activation and repression. We found that some genes responded to both intermittent and continuous Msn2 nuclear occupancy while others responded only to continuous occupancy. Finally, these studies document a dynamic interplay between nucleosomes and Msn2 such that nucleosomes can restrict access of Msn2 to its canonical binding sites while Msn2 can promote reposition, expulsion and recruitment of nucleosomes to alter gene expression. This interplay may allow the cell to discriminate between different types of stress signaling.

  • 18.
    Elfving, Nils
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Davoine, Céline
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Benlloch, Reyes
    Blomberg, Jeanette
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Brännström, Kristoffer
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Müller, Dörte
    Nilsson, Anders
    Ulfstedt, Mikael
    Ronne, Hans
    Wingsle, Gunnar
    Nilsson, Ove
    Björklund, Stefan
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    The Arabidopsis thaliana Med25 mediator subunit integrates environmental cues to control plant development2011Ingår i: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 108, nr 20, s. 8245-8250Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Development in plants is controlled by abiotic environmental cues such as day length, light quality, temperature, drought, and salinity. These signals are sensed by a variety of systems and transmitted by different signal transduction pathways. Ultimately, these pathways are integrated to control expression of specific target genes, which encode proteins that regulate development and differentiation. The molecular mechanisms for such integration have remained elusive. We here show that a linear 130-amino-acids-long sequence in the Med25 subunit of the Arabidopsis thaliana Mediator is a common target for the drought response element binding protein 2A, zinc finger homeodomain 1, and Myb-like transcription factors which are involved in different stress response pathways. In addition, our results show that Med25 together with drought response element binding protein 2A also function in repression of PhyB-mediated light signaling and thus integrate signals from different regulatory pathways.

  • 19. Fallath, Thorya
    et al.
    Kidd, Brendan N.
    Stiller, Jiri
    Davoine, Celine
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Umeå Plant Science Centre (UPSC).
    Björklund, Stefan
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Umeå Plant Science Centre (UPSC).
    Manners, John M.
    Kazan, Kemal
    Schenk, Peer M.
    MEDIATOR18 and MEDIATOR20 confer susceptibility to Fusarium oxysporum in Arabidopsis thaliana2017Ingår i: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 12, nr 4, artikel-id e0176022Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The conserved protein complex known as Mediator conveys transcriptional signals by acting as an intermediary between transcription factors and RNA polymerase II. As a result, Mediator subunits play multiple roles in regulating developmental as well as abiotic and biotic stress pathways. In this report we identify the head domain subunits MEDIATOR18 and MEDIATOR20 as important susceptibility factors for Fusarium oxysporum infection in Arabidopsis thaliana. Mutants of MED18 and MED20 display down-regulation of genes associated with jasmonate signaling and biosynthesis while up-regulation of salicylic acid associated pathogenesis related genes and reactive oxygen producing and scavenging genes. We propose that MED18 and MED20 form a sub-domain within Mediator that controls the balance of salicylic acid and jasmonate associated defense pathways.

  • 20. Filatov, D
    et al.
    Björklund, Stefan
    Umeå universitet, Medicinsk fakultet, Medicinsk kemi och biofysik.
    Johansson, Erik
    Umeå universitet, Medicinsk fakultet, Medicinsk kemi och biofysik.
    Thelander, Lars
    Umeå universitet, Medicinsk fakultet, Medicinsk kemi och biofysik.
    Induction of the mouse ribonucleotide reductase R1 and R2 genes in response to DNA damage by UV light.1996Ingår i: Journal of Biological Chemistry, ISSN 0021-9258, Vol. 271, nr 39, s. 23698-704Artikel i tidskrift (Refereegranskat)
  • 21. Frontini, M
    et al.
    Kotova, Irina
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Björklund, Stefan
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Mantovani, R
    Mechanisms of transcriptional activation of the AdML promoter by NF-Y.Manuskript (Övrigt vetenskapligt)
  • 22.
    Hallberg, Magnus
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Hu, Guo-Zhen
    Balciunas, Darius
    Sheikhibrahim, Zaki
    Björklund, Stefan
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Functional and physical interactions of the Mediator subunit Med21/Srb7Manuskript (Övrigt vetenskapligt)
  • 23.
    Hallberg, Magnus
    et al.
    Umeå universitet, Medicinsk fakultet, Medicinsk kemi och biofysik.
    Hu, Guo-Zhen
    Tronnersjö, Susanna
    Shaikhibrahim, Zaki
    Umeå universitet, Medicinsk fakultet, Medicinsk kemi och biofysik.
    Balciunas, Darius
    Björklund, Stefan
    Umeå universitet, Medicinsk fakultet, Medicinsk kemi och biofysik.
    Ronne, Hans
    Umeå universitet, Medicinsk fakultet, Medicinsk kemi och biofysik.
    Functional and physical interactions within the middle domain of the yeast mediator2006Ingår i: Molecular Genetics and Genomics, ISSN 1617-4615, E-ISSN 1617-4623, Vol. 276, nr 2, s. 197-210Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Med21 (Srb7) is a small essential subunit of the middle domain of the Mediator, which is conserved in all eukaryotes. It is thought to play an important role in both transcriptional activation and repression. In the yeast Saccharomyces cerevisiae, Med21 is known to interact both with the Mediator subunit Med6 and the global co-repressor Tup1. We have made a temperature-sensitive med21-ts mutant, which we used in a high copy number suppressor screen. We found ten yeast genes that can suppress the med21-ts mutation in high copy number. The three strongest suppressors were MED7 and MED10 (NUT2), which encode other Mediator subunits, and ASH1, which encodes a repressor of the HO gene. 2-Hybrid experiments confirmed multiple interactions between Med21, Med10, Med7 and Med4, and also revealed a Med21 self-interaction. The interactions of Med21 with Med7 and Med10 were verified by co-immunoprecipitation of tagged proteins produced in insect cells and E. coli, where both interactions were found to depend strongly on the amino acid residues 2-8 of Med21. These interactions, and the interactions of Med21 with Med6 and Tup1, suggest that Med21 may serve as a molecular switchboard that integrates different signals before they reach the core polymerase.

  • 24.
    Hallberg, Magnus
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Polozkov, Gennady
    Deluen, Cécile
    Collart, Martine
    Björklund, Stefan
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Phosphorylation of Serine 208 in Med2 is important for proper expression of genes required for anaerobic growth and purine and glykogen metabolismManuskript (Övrigt vetenskapligt)
  • 25.
    Hallberg, Magnus
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Polozkov, Gennady
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Hu, Guo-Zhen
    Beve, Jenny
    Gustafsson, Claes M.
    Ronne, Hans
    Björklund, Stefan
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Site-specific Srb10-dependent phosphorylation of the yeast Mediator subunit Med2 regulates gene expression from the 2-microm plasmid2004Ingår i: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 101, nr 10, s. 3370-3375Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The yeast Mediator complex is required for transcriptional regulation both in vivo and in vitro, and its function is conserved in all eukaryotes. Mediator interacts with both transcriptional activators and RNA polymerase II, but little is known about the mechanisms by which it operates at the molecular level. Here, we show that the cyclin-dependent kinase Srb10 interacts with, and phosphorylates, the Med2 subunit of Mediator both in vivo and in vitro. A point mutation of the single phosphorylation site in Med2 results in a strongly reduced expression of the REP1, REP2, FLP1, and RAF1 genes, which are all located on the endogenous 2-microm plasmid. Combined with previous studies on the effects of SRB10/SRB11 deletions, our data suggest that posttranslational modifications of Mediator subunits are important for regulation of gene expression.

  • 26.
    Johansson, Erik
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Björklund, Stefan
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Thelander, Lars
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Gene structure and regulation of the expression of the R1 and R2 subunits of mouse ribonucleotide reductase.1994Ingår i: Advances in Experimental Medicine and Biology, ISSN 0065-2598, E-ISSN 2214-8019, Vol. 370, s. 721-4Artikel i tidskrift (Refereegranskat)
  • 27. Kim, Y J
    et al.
    Björklund, Stefan
    Li, Y
    Sayre, M H
    Kornberg, R D
    A multiprotein mediator of transcriptional activation and its interaction with the C-terminal repeat domain of RNA polymerase II.1994Ingår i: Cell, ISSN 0092-8674, E-ISSN 1097-4172, Vol. 77, nr 4, s. 599-608Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A mediator was isolated from yeast that enabled a response to the activator proteins GAL4-VP16 and GCN4 in a transcription system reconstituted with essentially homogeneous basal factors and RNA polymerase II. The mediator comprised some 20 polypeptides, including the three subunits of TFIIF and other polypeptides cross-reactive with antisera against GAL11, SUG1, SRB2, SRB4, SRB5, and SRB6 proteins. Mediator not only enabled activated transcription but also conferred 8-fold greater activity in basal transcription and 12-fold greater efficiency of phosphorylation of RNA polymerase II by the TFIIH-associated C-terminal repeat domain (CTD) kinase, indicative of mediator-CTD interaction. A holoenzyme form of RNA polymerase II was independently isolated that supported a response to activator proteins with purified basal factors. The holoenzyme proved to consist of mediator associated with core 12-subunit RNA polymerase II.

  • 28.
    Kotova, Irina
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Chabes, Anna Lena
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Lobov, Sergei
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Thelander, Lars
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Björklund, Stefan
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Sequences downstream of the transcription initiation site are important for proper initiation and regulation of mouse ribonucleotide reductase R2 gene transcription2003Ingår i: European Journal of Biochemistry, ISSN 0014-2956, E-ISSN 1432-1033, Vol. 270, nr 8, s. 1791-1801Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Ribonucleotide reductase is essential for the synthesis of all four dNTPs required for DNA replication. The enzyme is composed of two proteins, R1 and R2, which are both needed for activity. Expression of the R1 and R2 mRNAs is restricted to the S-phase of the cell cycle, but the R1 and R2 promoters show no obvious sequence homologies that could indicate coordination of transcription. Here we study initiation of transcription at the natural mouse R2 promoter, which contains an atypical TATA-box with the sequence TTTAAA, using a combination of in vivo reporter gene assays and in vitro transcription. Our results indicate that in constructs where sequences from the R2 5'-UTR are present, the mouse R2 TATA-box is dispensable both for unregulated, basal transcription from the R2 promoter and for S-phase specific activity. Instead, initiation of R2 transcription is directed by sequences downstream from the transcription start. We report that this region contains a conserved palindrome sequence that interacts with TAF(II)s. This interaction down-regulates basal transcription from the R2 promoter, both in the absence and in the presence of the TATA-box.

  • 29.
    Kotova, Irina
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Chabes, Anna Lena
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Segerman, Bo
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Flodell, Sara
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Thelander, Lars
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Björklund, Stefan
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    A mouse in vitro transcription system reconstituted from highly purified RNA polymerase II, TFIIH, and recombinant TBP, TFIIB, TFIIE and TFIIF.2001Ingår i: European Journal of Biochemistry, ISSN 0014-2956, E-ISSN 1432-1033, Vol. 268, nr 16, s. 4527-4536Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Unregulated transcription of protein-encoding genes in vitro is dependent on 12-subunit core RNA polymerase II and five general transcription factors; TATA binding protein (TBP), transcription factor (TF)IIB, TFIIE, TFIIF, and TFIIH. Here we describe cloning of the mouse cDNAs encoding TFIIB and the small and large TFIIE and TFIIF subunits. The cDNAs have been used to express the corresponding proteins in recombinant form in Escherichia coli and in Sf21 insect cells, and all proteins have been purified to > 90% homogeneity. We have also purified a recombinant His6-tagged mouse TBP to near homogeneity and show that it is active in both a reconstituted mouse in vitro transcription system and a TBP-dependent in vitro transcription system from Saccharomyces cerevisiae. The more complex general transcription factors, TFIIH and RNA polymerase II, were purified more than 1000-fold and to near homogeneity, respectively, from tissue cultured mouse cells. When combined, the purified factors were sufficient to initiate transcription from different promoters in vitro. Functional studies of the S-phase-specific mouse ribonucleotide reductase R2 promoter using both the highly purified system described here (a mouse cell nuclear extract in vitro transcription system) and in vivo R2-promoter reporter gene assays together identify an NF-Y interacting promoter proximal CCAAT-box as being essential for high-level expression from the R2 promoter.

  • 30.
    Kumar, Koppolu Raja Rajesh
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Umeå Plant Science Centre (UPSC). Department of Biotechnology, Indira Gandhi National Tribal University (IGNTU), Amarkantak-484887, Madhya Pradesh,India.
    Blomberg, Jeanette
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Umeå Plant Science Centre (UPSC).
    Björklund, Stefan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Umeå Plant Science Centre (UPSC).
    The MED7 subunit paralogs of Mediator function redundantly in development of etiolated seedlings in Arabidopsis2018Ingår i: The Plant Journal, ISSN 0960-7412, E-ISSN 1365-313X, Vol. 96, nr 3, s. 578-594Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    MED7 is a subunit of the Mediator middle module and is encoded by two paralogs in Arabidopsis. We generated MED7 silenced lines using RNAi to study its impact on Arabidopsis growth and development. Compared with wild type, etiolated seedlings of the MED7 silenced lines exhibited reduced hypocotyl length caused by reduced cell elongation when grown in the dark. The hypocotyl length phenotype was rescued by exogenously supplied brassinosteroid. In addition, MED7 silenced seedlings exhibited defective hook opening in the dark as well as defective cotyledon expansion in the presence of the brassinosteroid inhibitor brassinazole. Whole transcriptome analysis on etiolated seedlings using RNA sequencing revealed several genes known to be regulated by auxin and brassinosteroids, and a broad range of cell wall-related genes that were differentially expressed in the MED7 silenced lines. This was especially evident for genes involved in cell wall extension and remodeling, such as EXPANSINs and XTHs. Conditional complementation with each MED7 paralog individually restored the hypocotyl phenotype as well as the gene expression defects. Additionally, conditional expression of MED7 had no effects that were independent of the Mediator complex on the observed phenotypes. We concluded that the MED7 paralogs function redundantly in regulating genes required for the normal development of etiolated Arabidopsis seedlings.

  • 31.
    Larsson, Miriam
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Uvell, Hanna
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Sandström, Jenny
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Rydén, Patrik
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för matematik och matematisk statistik.
    Selth, Luke A.
    Mechanisms of Transcription Laboratory, Clare Hall Laboratories, Cancer Research UK London Research Institute.
    Björklund, Stefan
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Functional Studies of the Yeast Med5, Med15 and Med16 Mediator Tail Subunits2013Ingår i: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 8, nr 8, s. e73137-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The yeast Mediator complex can be divided into three modules, designated Head, Middle and Tail. Tail comprises the Med2, Med3, Med5, Med15 and Med16 protein subunits, which are all encoded by genes that are individually non-essential for viability. In cells lacking Med16, Tail is displaced from Head and Middle. However, inactivation of MED5/MED15 and MED15/MED16 are synthetically lethal, indicating that Tail performs essential functions as a separate complex even when it is not bound to Middle and Head. We have used the N-Degron method to create temperature-sensitive (ts) mutants in the Mediator tail subunits Med5, Med15 and Med16 to study the immediate effects on global gene expression when each subunit is individually inactivated, and when Med5/15 or Med15/16 are inactivated together. We identify 25 genes in each double mutant that show a significant change in expression when compared to the corresponding single mutants and to the wild type strain. Importantly, 13 of the 25 identified genes are common for both double mutants. We also find that all strains in which MED15 is inactivated show down-regulation of genes that have been identified as targets for the Ace2 transcriptional activator protein, which is important for progression through the G1 phase of the cell cycle. Supporting this observation, we demonstrate that loss of Med15 leads to a G1 arrest phenotype. Collectively, these findings provide insight into the function of the Mediator Tail module.

  • 32. Li, Y
    et al.
    Bjorklund, Stefan
    Jiang, Y W
    Kim, Y J
    Lane, W S
    Stillman, D J
    Kornberg, R D
    Yeast global transcriptional regulators Sin4 and Rgr1 are components of mediator complex/RNA polymerase II holoenzyme.1995Ingår i: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 92, nr 24, s. 10864-8Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Sin4 and Rgr1 proteins, previously shown by genetic studies to play both positive and negative roles in the transcriptional regulation of many genes, are identified here as components of mediator and RNA polymerase II holoenzyme complexes. Results with Sin4 deletion and Rgr1 truncation strains indicate the association of these proteins in a subcomplex comprising Sin4, Rgr1, Gal11, and a 50-kDa polypeptide. Taken together with the previous genetic evidence, our findings point to a role of the mediator in repression as well as in transcriptional activation.

  • 33. Li, Y
    et al.
    Bjorklund, Stefan
    Kim, Y J
    Kornberg, R D
    Yeast RNA polymerase II holoenzyme.1996Ingår i: Methods in Enzymology, ISSN 0076-6879, E-ISSN 1557-7988, Vol. 273, s. 172-5Artikel i tidskrift (Refereegranskat)
  • 34. Poon, D
    et al.
    Bai, Y
    Campbell, A M
    Bjorklund, Stefan
    Kim, Y J
    Zhou, S
    Kornberg, R D
    Weil, P A
    Identification and characterization of a TFIID-like multiprotein complex from Saccharomyces cerevisiae.1995Ingår i: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 92, nr 18, s. 8224-8Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Although the mechanisms of transcriptional regulation by RNA polymerase II are apparently highly conserved from yeast to man, the identification of a yeast TATA-binding protein (TBP)-TBP-associated factor (TAFII) complex comparable to the metazoan TFIID component of the basal transcriptional machinery has remained elusive. Here, we report the isolation of a yeast TBP-TAFII complex which can mediate transcriptional activation by GAL4-VP16 in a highly purified yeast in vitro transcription system. We have cloned and sequenced the genes encoding four of the multiple yeast TAFII proteins comprising the TBP-TAFII multisubunit complex and find that they are similar at the amino acid level to both human and Drosophila TFIID subunits. Using epitope-tagging and immunoprecipitation experiments, we demonstrate that these genes encode bona fide TAF proteins and show that the yeast TBP-TAFII complex is minimally composed of TBP and seven distinct yTAFII proteins ranging in size from M(r) = 150,000 to M(r) = 25,000. In addition, by constructing null alleles of the cloned TAF-encoding genes, we show that normal function of the TAF-encoding genes is essential for yeast cell viability.

  • 35. Shaikhali, Jehad
    et al.
    Davoine, Celine
    Brännström, Kristoffer
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Umeå Plant Science Centre (UPSC).
    Rouhier, Nicolas
    Bygdell, Joakim
    Björklund, Stefan
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Umeå Plant Science Centre (UPSC).
    Wingsle, Gunnar
    Biochemical and redox characterization of the mediator complex and its associated transcription factor GeBPL, a GLABROUS1 enhancer binding protein2015Ingår i: Biochemical Journal, ISSN 0264-6021, E-ISSN 1470-8728, Vol. 468, nr 3, s. 385-400Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The eukaryotic mediator integrates regulatory signals from promoter-bound transcription factors (TFs) and transmits them to RNA polymerase II (Pol II) machinery. Although redox signalling is important in adjusting plant metabolism and development, nothing is known about a possible redox regulation of mediator. In the present study, using pull-down and yeast two-hybrid assays, we demonstrate the association of mediator (MED) subunits MED10a, MED28 and MED32 with the GLABROUS1 (GL1) enhancer-binding protein-like (GeBPL), a plant-specific TF that binds a promoter containing cryptochrome 1 response element 2 (CryR2) element. All the corresponding recombinant proteins form various types of covalent oligomers linked by intermolecular disulfide bonds that are reduced in vitro by the thioredoxin (TRX) and/or glutathione/glutaredoxin (GRX) systems. The presence of recombinant MED10a, MED28 and MED32 subunits or changes of its redox state affect the DNA-binding capacity of GeBPL suggesting that redox-driven conformational changes might modulate its activity. Overall, these results advance our understanding of how redox signalling affects transcription and identify mediator as a novel actor in redox signalling pathways, relaying or integrating redox changes in combinationwith specific TFs as GeBPL.

  • 36. Shaikhali, Jehad
    et al.
    Davoine, Céline
    Björklund, Stefan
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Umeå Plant Science Centre (UPSC).
    Wingsle, Gunnar
    Redox regulation of the MED28 and MED32 mediator subunits is important for development and senescence2016Ingår i: Protoplasma, ISSN 0033-183X, E-ISSN 1615-6102, Vol. 253, nr 3, s. 957-963Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Mediator is a conserved multi-protein complex that acts as a bridge between promoter-bound transcriptional regulators and RNA polymerase II. While redox signaling is important in adjusting plant metabolism and development, the involvement of Mediator in redox homeostasis and regulation only recently started to emerge. Our previous results show that the MED10a, MED28, and MED32 Mediator subunits form various types of covalent oligomers linked by intermolecular disulfide bonds in vitro. To link that with biological significance we have characterized Arabidopsis med32 and med28 mutants and found that they are affected in root development and senescence, phenotypes possibly associated to redox changes.

  • 37.
    Shaikhibrahim, Zaki
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Rahaman, Hamidur
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Wittung-Stafshede, Pernilla
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Björklund, Stefan
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Med8, Med18, and Med20 subunits of the Mediator head domain are interdependent upon each other for folding and complex formation2009Ingår i: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 106, nr 49, s. 20728-20733Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We have studied folding and complex formation of the yeast mediator head-module protein subunits Med8, Med18, and Med20. Using a combination of immunoprecipitation, far-UV circular dichroism, and fluorescence measurements on recombinantly expressed and denatured proteins that were allowed to renature separately or in different combinations, we found that Med8, Med18, and Med20 can fold in different ways to form both soluble monomeric proteins and different distinct subcomplexes. However, the concurrent presence of all three protein subunits during the renaturation process is required for proper folding and trimer complex formation.

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