3大种群蛋白质内部重复片段组成规律的比较研究

20世纪70年代，Ohno提出了功能蛋白的起源理论，认为寡肽片段的周期性重复是蛋白质起源的一种方式。蛋白质内部重复片段在蛋白质序列进化的过程中具有重要意义。选取原核生物、古细菌、真核生物的8个代表物种，设计了新的蛋白质内部重复片段的提取方法，并用矩阵的方式对重复片段的类型及其出现的频率进行形象地展现，既保留了重复片段的序列特征又可进行全局性的统计描述。分析表明：真核生物高频率的使用简单重复序列；真细菌也具有低频率使用简单重复序列的现象；而古细菌则几乎没有。进一步研究显示，3大种群生物偏向性使用氨基酸构成蛋白质内部重复片段的形为与蛋白质组的氨基酸使用频率紧密相关。其相关系数在真细菌和古细菌中高于0．95，而真核生物略低。真核生物蛋白质组大量使用简单重复片段，以及两者在氨基酸使用上的较低相关性暗示简单重复序列的快速进化是导致真核生物蛋白质组高复杂性的一个关键因素。

Comparative Analysis of Internal Repeating Segments in Proteins of Species from the Three Kingdoms of Life

In 1970's,Ohno proposed that primordial proteins might evolve from periodic amplification of oligo-peptides.Internal repeating segments in proteins may play important roles in functional evolution of proteins.In this study,a new method was designed to extract internal repeating segments from proteomes of 8 modern species belong to eukaryota,bacteria and archaea,respectively.The repeating patterns and the frequencies within proteomes of each kingdom were analyzed by matrix plot.Simple repeat segments were found in eukaryotic proteins with high frequencies,but were much lower in bacteria and none in archaea.Further analysis showed that,the biased usage of amino acids in the internal repeating segments was positively related to the frequencies of individual amino acids in the proteome of a given species.The correlation coefficient was up to 0.95 in prokaryota,with the eukaryota to be lower.The high frequency of simple repeat sequences in eukaryotic proteomes,as well as the disparate relationships of amino acid compositions between the internal repeating segments and their haboring eukaryotic proteomes imply that the fast evolution of simple repeat sequences could be one force that generates the high complexity of eukarytic proteomes.