Kunisawa T, Horimoto K, Otsuka J
J Mol Evol. 1987;24(4):357-65. doi: 10.1007/BF02134134.
A simple method for the evolutionary analysis of amino acid sequence data is presented and used to examine whether the number of variable sites (NVS) of a protein is constant during its evolution. The NVSs for hemoglobin and for mitochondrial cytochrome c are each found to be almost constant, and the ratio between the NVSs is close to the ratio between the unit evolutionary periods. This indicates that the substitution rate per variable site is almost uniform for these proteins, as the neutral theory claims. An advantage of the present analysis is that it can be done without knowledge of paleontological divergence times and can be extended to bacterial proteins such as bacterial c-type cytochromes. It is suggested that the NVS of cytochrome c has been almost constant even over the long period (ca. 3.0 billion years) of bacterial evolution but that at least two different substitution rates are necessary to describe the accumulated changes in the sequence. This "two clock" interpretation is consistent with fossil evidence for the appearance times of photosynthetic bacteria and eukaryotes.
本文提出了一种用于氨基酸序列数据进化分析的简单方法，并用于检验蛋白质的可变位点数量（NVS）在其进化过程中是否恒定。结果发现，血红蛋白和线粒体细胞色素c的NVS各自几乎恒定，且NVS之间的比率接近单位进化周期之间的比率。这表明，如中性理论所主张的，这些蛋白质每个可变位点的替换率几乎是均匀的。本分析的一个优点是，无需了解古生物学分歧时间即可进行，并且可以扩展到细菌蛋白质，如细菌c型细胞色素。有人提出，即使在细菌进化的漫长时期（约30亿年），细胞色素c的NVS也几乎恒定，但描述序列中的累积变化至少需要两种不同的替换率。这种“双时钟”解释与光合细菌和真核生物出现时间的化石证据一致。
