Hayashida H, Toh H, Kikuno R, Miyata T
Department of Biology, Faculty of Science, Kyushu University.
Mol Biol Evol. 1985 Jul;2(4):289-303. doi: 10.1093/oxfordjournals.molbev.a040352.
The nucleotide sequences of the eight different influenza A virus segments (genes) were compared among 14 different subtypes. These comparisons demonstrate the presence of molecular clocks in the viral genes; they accumulated both silent and amino acid-changing substitutions at approximately constant rates with respect to time during evolution. In addition, comparison of the rates of evolution among the eight viral genes, excluding the P2 gene, revealed a rapid and roughly equal rate of silent substitution for different genes. The P2 gene exception is explained as the result of recombination (reassortment) between distantly related strains. The rate of amino acid-changing substitution differs greatly from gene to gene. The rate of silent substitution was estimated to be 1.1 X 10(-2)/site/year on the average--that is, about 2 X 10(6) times higher than eukaryotic gene equivalents, which is remarkable. Strain A/USSR/90/77 was shown to evolve with a rate that is similar to those of other strains but to behave as if replication was frozen during a certain period (Nakajima et al. 1978). The frozen period was estimated to be 25 yr on the basis of the molecular clock. A similar analysis revealed another example of frozen replication--in this case, apparently for a period of about 9 yr--in a duck strain, A/duck/Ontario/77.
在14种不同的甲型流感病毒亚型中，对8个不同的甲型流感病毒片段（基因）的核苷酸序列进行了比较。这些比较证明了病毒基因中存在分子钟；在进化过程中，它们以大致恒定的速率积累沉默替换和氨基酸替换。此外，对8个病毒基因（不包括P2基因）的进化速率进行比较，发现不同基因的沉默替换速率快速且大致相等。P2基因的例外情况被解释为远缘菌株之间重组（重配）的结果。氨基酸替换速率在不同基因之间差异很大。沉默替换速率平均估计为1.1×10⁻²/位点/年——也就是说，比真核基因等效物高约2×10⁶倍，这很显著。A/USSR/90/77毒株的进化速率与其他毒株相似，但表现得好像在某个时期复制被冻结了（中岛等人，1978年）。根据分子钟，冻结期估计为25年。类似的分析揭示了另一个复制冻结的例子——在这种情况下，显然是在一个鸭毒株A/duck/Ontario/77中，冻结期约为9年。
