Doolittle R F
Center for Molecular Genetics University of California, San Diego, La Jolla, 92093-0634, USA.
Annu Rev Biochem. 1995;64:287-314. doi: 10.1146/annurev.bi.64.070195.001443.
The domainal nature of proteins is well established. What is less certain is how many domains are evolutionarily mobile in that they occur in otherwise nonhomologous proteins or in different sequential locations in homologous proteins. The combinatorial advantage of shuffling domains around into diverse settings is obvious. Those domains that have been shuffled about in recent evolutionary times, within the last half billion years or so, can usually be identified on the basis of sequence resemblances alone. Contrarily, domains that were rearranged in ancient times may only be apparent after three-dimensional analysis, their sequence resemblances having been eroded over time. The shuffling of domains in recently evolved proteins has been greatly promoted by introns, but this does not imply that all domainal rearrangements involve introns. Only a small fraction of known exons show evidence of having been shuffled. Taken in aggregate, the available data best fit a scenario whereby a relative small number of genes encoding domain-sized polypeptides has been expanded by duplication and modification with a burst of exceptional genomic rearrangement.
蛋白质的结构域性质已得到充分证实。尚不确定的是，有多少结构域在进化过程中是可移动的，即它们出现在其他非同源蛋白质中，或同源蛋白质的不同序列位置上。将结构域重新组合到不同环境中的组合优势是显而易见的。那些在最近的进化时期，即在大约过去的5亿年里被重新排列的结构域，通常仅根据序列相似性就能识别出来。相反，古代重新排列的结构域可能只有在三维分析之后才会显现出来，它们的序列相似性随着时间的推移已经被侵蚀。内含子极大地促进了最近进化的蛋白质中结构域的重排，但这并不意味着所有的结构域重排都涉及内含子。已知的外显子中只有一小部分显示出被重排的证据。总体而言，现有数据最符合这样一种情况：通过重复和修饰，以及一系列特殊的基因组重排，相对少数编码结构域大小多肽的基因得到了扩展。
