Hughes A L
Department of Biology, Pennsylvania State University, University Park 16802.
Proc Biol Sci. 1994 May 23;256(1346):119-24. doi: 10.1098/rspb.1994.0058.
A widely cited model of the evolution of functionally novel proteins (here called the model of mutation during non-functionality (MDN model)) holds that, after gene duplication, one gene copy is redundant and free to accumulate substitutions at random. By chance, some of these substitutions may suit the protein encoded by such a non-functional gene to a new function, which it can subsequently assume. Several lines of evidence contradict this hypothesis: (i) comparison of expressed duplicate genes from the tetraploid frog Xenopus laevis suggests that such genes are subject to purifying selection and are thus not free to accumulate substitutions at random; (ii) in a number of multi-gene families, there is now evidence that functionally distinct proteins have arisen not as a result of chance fixation of neutral variants but rather as a result of positive Darwinian selection; and (iii) the phenomenon of gene sharing, in which a single gene encodes a protein having two distinct functions, shows that gene duplication is not a necessary prerequisite to the evolution of a new protein function. A model for the evolution of new protein is proposed under which a period of gene sharing ordinarily precedes the evolution of functionally distinct proteins. Gene duplication then allows each daughter gene to specialize for one of the functions of the ancestral gene.(ABSTRACT TRUNCATED AT 250 WORDS)
一个被广泛引用的关于功能新颖蛋白质进化的模型（这里称为无功能期突变模型，即MDN模型）认为，基因复制后，一个基因拷贝是冗余的，可以随机积累替换。偶然地，这些替换中的一些可能使由这样一个无功能基因编码的蛋白质适合一种新功能，随后它可以承担这种新功能。几条证据与这一假设相矛盾：（i）对四倍体青蛙非洲爪蟾中表达的重复基因进行比较表明，这些基因受到纯化选择，因此不能随机积累替换；（ii）在许多多基因家族中，现在有证据表明，功能不同的蛋白质并非由于中性变体的偶然固定而产生，而是由于正向达尔文选择；（iii）基因共享现象，即单个基因编码具有两种不同功能的蛋白质，表明基因复制不是新蛋白质功能进化的必要前提。提出了一种新蛋白质进化模型，在该模型中，功能不同的蛋白质进化之前通常会有一段基因共享期。然后基因复制使每个子基因专门负责祖先基因的一种功能。（摘要截于250字）
