Begun D J
Section of Evolution and Ecology, University of California, Davis 95616, USA.
Genetics. 1997 Feb;145(2):375-82. doi: 10.1093/genetics/145.2.375.
Drosophila alcohol dehydrogenase (Adh) is highly conserved in size, organization, and amino acid sequence. Adh-psi was hypothesized to be a pseudogene derived from an Adh duplication in the repleta group of Drosophila; however, several results from molecular analyses of this gene conflict with currently held notions of molecular evolution. Perhaps the most difficult observations to reconcile with the pseudogene hypothesis are that the hypothetical replacement sites of Adh-psi evolve only slightly more quickly than replacement sites of closely related, functional Adh genes, and that the replacement sites of the pseudogenes evolve considerably more slowly than neighboring silent sites. The data have been presented as a paradox that challenges our understanding of the mechanisms underlying DNA sequence divergence. Here I show that Adh-psi is actually a new, functional gene recently descended from an Adh duplication. This descendant recruited approximately 60 new N-terminal amino acids, is considerably more basic than ADH, and is evolving at a faster rate than Adh. Furthermore, though the descendant is clearly functional, as inferred from molecular evolution and population genetic data, it retains no obvious ADH activity. This probably reflects functional divergence from its Adh ancestor.
果蝇乙醇脱氢酶（Adh）在大小、结构和氨基酸序列方面高度保守。Adh-psi被推测为果蝇repleta组中Adh基因重复产生的假基因；然而，对该基因进行分子分析得到的几个结果与当前分子进化的观点相冲突。也许与假基因假说最难调和的观察结果是，Adh-psi的假定替代位点的进化速度仅比密切相关的功能性Adh基因的替代位点略快，而且假基因的替代位点的进化速度比相邻的沉默位点慢得多。这些数据被视为一个悖论，挑战了我们对DNA序列差异潜在机制的理解。在这里，我表明Adh-psi实际上是一个最近从Adh基因重复中衍生出来的新的功能性基因。这个衍生物招募了大约60个新的N端氨基酸，比ADH碱性强得多，并且进化速度比Adh快。此外，尽管从分子进化和群体遗传学数据推断该衍生物显然具有功能，但它没有明显的ADH活性。这可能反映了它与其Adh祖先的功能差异。
