Sharp P M
Department of Genetics, Trinity College, Dublin, Ireland.
J Mol Evol. 1991 Jul;33(1):23-33. doi: 10.1007/BF02100192.
The nature and extent of DNA sequence divergence between homologous protein-coding genes from Escherichia coli and Salmonella typhimurium have been examined. The degree of divergence varies greatly among genes at both synonymous (silent) and nonsynonymous sites. Much of the variation in silent substitution rates can be explained by natural selection on synonymous codon usage, varying in intensity with gene expression level. Silent substitution rates also vary significantly with chromosomal location, with genes near oriC having lower divergence. Certain genes have been examined in more detail. In particular, the duplicate genes encoding elongation factor Tu, tufA and tufB, from S. typhimurium have been compared to their E. coli homologues. As expected these very highly expressed genes have high codon usage bias and have diverged very little between the two species. Interestingly, these genes, which are widely spaced on the bacterial chromosome, also appear to be undergoing concerted evolution, i.e., there has been exchange between the loci subsequent to the divergence of the two species.
人们已经研究了大肠杆菌和鼠伤寒沙门氏菌同源蛋白质编码基因之间DNA序列差异的性质和程度。在同义（沉默）位点和非同义位点上，不同基因之间的差异程度差异很大。沉默替代率的大部分变化可以通过对同义密码子使用的自然选择来解释，其强度随基因表达水平而变化。沉默替代率也随染色体位置而显著变化，oriC附近的基因具有较低的差异。已经对某些基因进行了更详细的研究。特别是，将鼠伤寒沙门氏菌中编码延伸因子Tu的重复基因tufA和tufB与其大肠杆菌同源物进行了比较。正如预期的那样，这些高表达基因具有很高的密码子使用偏好，并且在两个物种之间差异很小。有趣的是，这些在细菌染色体上相距很远的基因似乎也在经历协同进化，即在两个物种分化之后，基因座之间发生了交换。
