Ikemura T
Department of Biophysics, Faculty of Science, Kyoto University, Japan.
Mol Biol Evol. 1985 Jan;2(1):13-34. doi: 10.1093/oxfordjournals.molbev.a040335.
Choices of synonymous codons in unicellular organisms are here reviewed, and differences in synonymous codon usages between Escherichia coli and the yeast Saccharomyces cerevisiae are attributed to differences in the actual populations of isoaccepting tRNAs. There exists a strong positive correlation between codon usage and tRNA content in both organisms, and the extent of this correlation relates to the protein production levels of individual genes. Codon-choice patterns are believed to have been well conserved during the course of evolution. Examination of silent substitutions and tRNA populations in Enterobacteriaceae revealed that the evolutionary constraint imposed by tRNA content on codon usage decelerated rather than accelerated the silent-substitution rate, at least insofar as pairs of taxonomically related organisms were examined. Codon-choice patterns of multicellular organisms are briefly reviewed, and diversity in G+C percentage at the third position of codons in vertebrate genes--as well as a possible causative factor in the production of this diversity--is discussed.
本文综述了单细胞生物中同义密码子的选择情况，并指出大肠杆菌和酿酒酵母之间同义密码子使用的差异归因于同工tRNA实际数量的不同。在这两种生物中，密码子使用与tRNA含量之间均存在强正相关，且这种相关性的程度与各个基因的蛋白质生产水平相关。密码子选择模式在进化过程中被认为得到了很好的保守。对肠杆菌科沉默替换和tRNA群体的研究表明，至少就分类学上相关的生物对而言，tRNA含量对密码子使用所施加的进化限制减缓而非加速了沉默替换率。本文还简要综述了多细胞生物的密码子选择模式，并讨论了脊椎动物基因中密码子第三位G+C百分比的多样性以及产生这种多样性的一个可能因素。
