Liao D
Department of Microbiology and Infectious Diseases, Faculty of Medicine, Université de Sherbrooke, Sherbrooke, 3001 12e Avenue Nord, Québec, J1H 5N4 Canada.
J Mol Evol. 2000 Oct;51(4):305-17. doi: 10.1007/s002390010093.
Multiple copies of a given ribosomal RNA gene family undergo concerted evolution such that sequences of all gene copies are virtually identical within a species although they diverge normally between species. In eukaryotes, gene conversion and unequal crossing over are the proposed mechanisms for concerted evolution of tandemly repeated sequences, whereas dispersed genes are homogenized by gene conversion. However, the homogenization mechanisms for multiple-copy, normally dispersed, prokaryotic rRNA genes are not well understood. Here we compared the sequences of multiple paralogous rRNA genes within a genome in 12 prokaryotic organisms that have multiple copies of the rRNA genes. Within a genome, putative sequence conversion tracts were found throughout the entire length of each individual rRNA genes and their immediate flanks. Individual conversion events convert only a short sequence tract, and the conversion partners can be any paralogous genes within the genome. Interestingly, the genic sequences undergo much slower divergence than their flanking sequences. Moreover, genomic context and operon organization do not affect rRNA gene homogenization. Thus, gene conversion underlies concerted evolution of bacterial rRNA genes, which normally occurs within genic sequences, and homogenization of flanking regions may result from co-conversion with the genic sequence.
给定核糖体RNA基因家族的多个拷贝会经历协同进化，以至于在一个物种内所有基因拷贝的序列实际上是相同的，尽管它们在不同物种之间通常会发生分歧。在真核生物中，基因转换和不等交换是串联重复序列协同进化的推测机制，而分散的基因则通过基因转换实现同质化。然而，对于多拷贝、通常分散的原核生物rRNA基因的同质化机制，人们还了解得不够透彻。在这里，我们比较了12种具有多个rRNA基因拷贝的原核生物基因组内多个旁系同源rRNA基因的序列。在一个基因组内，在每个单独的rRNA基因及其紧邻侧翼的整个长度上都发现了假定的序列转换区域。单个转换事件仅转换短的序列片段，并且转换伙伴可以是基因组内的任何旁系同源基因。有趣的是，基因序列的分歧比其侧翼序列要慢得多。此外，基因组背景和操纵子组织并不影响rRNA基因的同质化。因此，基因转换是细菌rRNA基因协同进化的基础，这种协同进化通常发生在基因序列内，侧翼区域的同质化可能是与基因序列共同转换的结果。
