Miyata T, Yasunaga T, Nishida T
Proc Natl Acad Sci U S A. 1980 Dec;77(12):7328-32. doi: 10.1073/pnas.77.12.7328.
Comparison of about 50 pairs of homologous nucleotide sequences for different genes revealed that the substitutions between synonymous codons occurred at much higher rates than did amino acid substitutions. Furthermore, five pairs of mRNA sequences for different genes were compared in species that had diverged at the same time. The evolutionary rate of synonymous substitution was estimated to be 5.1 X 10(-9) per site per year on the average and is approximately constant among different genes. It also is suggested that this property would be suitable for a molecular clock to determine the evolutionary relationships and branching order of duplicated genes. Each functional block of the noncoding region evolves with a rate that is almost constant, regardless of the types of genes. The intervening sequence and the 5' portion of the 3' noncoding region show considerable divergence, the extent of which is almost comparable to that in the synonymous codon sites, whereas the other blocks consisting of the 5' noncoding region and the 3' portion of the 3' noncoding region are strongly conserved, showing approximatley half of the divergence of the synonymous sites. This strong sequence preservation might be due to the functional requirements for transcription and modification of mRNA.
对约50对不同基因的同源核苷酸序列进行比较后发现，同义密码子之间的替换发生率远高于氨基酸替换。此外，在同时发生分化的物种中，对不同基因的五对mRNA序列进行了比较。同义替换的进化速率估计平均为每年每个位点5.1×10⁻⁹，并且在不同基因之间大致恒定。还表明，这一特性适用于分子钟，以确定重复基因的进化关系和分支顺序。非编码区的每个功能块以几乎恒定的速率进化，而与基因类型无关。间隔序列和3'非编码区的5'部分显示出相当大的差异，其程度几乎与同义密码子位点的差异相当，而由5'非编码区和3'非编码区的3'部分组成的其他块则高度保守，显示出约为同义位点差异一半的差异。这种强烈的序列保守性可能是由于mRNA转录和修饰的功能需求所致。
