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Thioredoxins are small thiol proteins that have a

conserved active site sequence, WCGPC, and reduce

disulfide bonds in various proteins using the two active site

cysteines, a reaction that oxidizes thioredoxin and renders it

inactive. Thioredoxin reductase returns thioredoxin to its

reduced, active form in a reaction that converts NADPH to

NADP+. The biological functions of thioredoxins vary

widely; they have roles in oxidative stress protection, act as

electron donors for ribonucleotide reductase, and form

structural components of enzymes. To date, three thioredoxin

genes have been characterized in Drosophila melanogaster:

the generally expressed Thioredoxin-2 (Trx-2) and the two

sex-specific genes ThioredoxinT (TrxT) and deadhead

(dhd). The male-specific TrxT and the female-specific dhd

are located as a gene pair, transcribed in opposite directions,

with only 470 bp between their transcription start points. We

show in this study that all three D. melanogaster thioredoxins

are conserved in 11 other Drosophilid species, which are

believed to have diverged up to 40 Ma ago and that Trx-2 is

conserved all the way to Tribolium castaneum. We have

found that the intriguing gene organization and regulation of

TrxT and dhd is remarkably well conserved and identified

potential conserved regulatory sequences. In addition, we

show that the 50–70 C terminal amino acids of TrxT constitute

a hyper-variable domain, which could play a role in

sexual conflict and male–female co-evolution.