Single-domain β-thymosins: the family history.

Evolution probably invented the β-thymosin domain in a single-celled close relative of multicellular animals. Expansion from single genes to the small family of monomeric β-thymosins of present-day vertebrates may have started with a very ancient duplication, before the rounds of whole-genome duplications. In land vertebrates and fish, this family consists of the descendants of five genes of their jawed vertebrate common ancestor. Identifying this common ancestry depends on the genes possessing conserved sets of flanking sequences, as the relationships are not recognizable from amino-acid sequences. One of these genes has given rise both to a group of fish β-thymosins and to a hitherto unrecognized group of β-thymosins of birds and reptiles. The resulting classification may prove useful in relation to the β-thymosins of model organisms, such as the zebrafish, and for identifying important noncoding sequence elements, exemplified here by a conserved sequence in the 3'untranslated region of transcripts from the β4 subfamily.
(© 2012 New York Academy of Sciences.)