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The rlmB Gene Is Essential for Formation of Gm2251 in 23S rRNA but Not for Ribosome Maturation in Escherichia coli
Umeå University, Faculty of Science and Technology, Department of Molecular Biology (Faculty of Science and Technology).
Umeå University, Faculty of Medicine, Molecular Biology.
2001 (English)In: Journal of Bacteriology, ISSN 0021-9193, E-ISSN 1098-5530, Vol. 183, no 23, 6957-6960 p.Article in journal (Refereed) Published
Abstract [en]

In Saccharomyces cerevisiae, the rRNA Gm2270 methyltransferase, Pet56p, has an essential role in the maturation of the mitochondrial large ribosomal subunit that is independent of its methyltransferase activity. Here we show that the proposed Escherichia coli ortholog, RlmB (formerly YjfH), indeed is essential for the formation of Gm in position 2251 of 23S rRNA. However, a DeltarlmB mutant did not show any ribosome assembly defects and was not outgrown by a wild-type strain even after 120 cell mass doublings. Thus, RlmB has no important role in ribosome assembly or function in E. coli.

Place, publisher, year, edition, pages
2001. Vol. 183, no 23, 6957-6960 p.
National Category
Medical and Health Sciences
URN: urn:nbn:se:umu:diva-4316DOI: 10.1128/JB.183.23.6957-6960.2001PubMedID: 11698387OAI: diva2:143346
Available from: 2004-12-15 Created: 2004-12-15 Last updated: 2010-08-06Bibliographically approved
In thesis
1. Accessory factors for ribosomal assembly
Open this publication in new window or tab >>Accessory factors for ribosomal assembly
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The assembly of ribosomal RNA (rRNA) and ribosomal proteins (r-proteins) into ribosomal subunits (30S and 50S) is a complex process. Transcription of rRNA requires antitermination proteins and the primary transcripts are processed by ribonucleases. R-proteins and rRNAs are chemically modified, the r-proteins bind to the rRNAs and the formed RNA-protein complexes are folded into mature ribosomal subunits. All these processes are well-coordinated and overlapping. Non-ribosomal factors are required for proper assembly and maturation of the ribosomal subunits. Two of these factors are the RimM and RbfA proteins, which bind to 30S subunits and are important for efficient processing of 16S rRNA. Lack of either RimM or RbfA results in a reduced amount of polysomes and a lower growth rate. An increased amount of RbfA can partially compensate for deficiencies shown by a RimM lacking mutant.

Here, mutations that alter phylogenetically conserved amino acids in RimM have been constructed. One of these (rimM120), which resulted in the replacement of two adjacent tyrosines by alanines, reduced the growth rate three-fold and also decreased the processing efficiency of 16S rRNA. The RimM120 mutant protein showed a much reduced binding to the 30S subunits. Suppression of the rimM120 mutant was achieved by increased amount of the RimM120 protein, by overexpression of rbfA, or by mutations that changed r-protein S19 or 16S rRNA. A variant of r-protein S13, which was previously isolated as a suppressor to a deletion of rimM (∆rimM), suppressed also the rimM120 mutation. The wild-type RimM protein, but not the RimM120 protein, was shown to bind r-protein S19 in the 30S subunits. The changes in S13, S19 and 16S rRNA that compensated for the deficiencies shown by the rimM mutants are all located within a small region of the head of the 30S subunit, suggesting that this region is the likely target for the RimM action.

To isolate RbfA variants that show reduced association with the 30S subunits, phylogenetically conserved, surface exposed amino acid residues of RbfA were changed to alanines or, in some instances, to amino acids of the opposite charge to that in the wild-type protein. Alterations of F5, R31, D46 and D100 had the largest effect on growth.

Mutations in the metY-nusA-infB operon, isolated as suppressors to the ∆rimM mutant, were shown to increase the amounts of RbfA. In a ∆rimM mutant, all RbfA protein was found associated with the 30S subunits and no free RbfA was detected.

The RlmB protein was shown to be the methyltransferase responsible for the formation of Gm2251 in 23S rRNA in Escherichia coli. Unlike a Saccharomyces cerevisiae mutant that lacks the orthologue to RlmB, Pet56p, which methylates mitochondrial rRNA, a ∆rlmB mutant did not show any defects in ribosomal assembly.

Place, publisher, year, edition, pages
Umeå: Molekylärbiologi (Teknisk-naturvetenskaplig fakultet), 2004. 57 p.
Molecular biology, RimM, RbfA, RlmB, ribosomal assembly, rRNA processing, Molekylärbiologi
National Category
Biochemistry and Molecular Biology
Research subject
Molecular Biology
urn:nbn:se:umu:diva-385 (URN)91-7305-783-5 (ISBN)
Public defence
2005-01-14, major groove, 6L, NUS, Institutionen för molekylärbiologi, 901 87 Umeå, Umeå, 13:00
Available from: 2004-12-15 Created: 2004-12-15 Last updated: 2010-08-06Bibliographically approved

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Lövgren, J. MattiasWikström, P. Mikael
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