Molecular evolutionary study of RNA viral genes.

本研究的目的是从分子进化的角度阐明RNA病毒的进化特征。特别是，我们研究了人类免疫缺陷病毒(HIV)和肿瘤病毒等RNA病毒的核苷酸替换率。我们发现，这些典型的逆转录病毒的替换率每年在每个站点10^-3；数量级。这些比率是包括核基因和线粒体基因在内的真核基因的106倍。虽然人类乙肝病毒不是一种RNA病毒，但我们也检测了乙肝病毒的核苷酸替换率。这是因为乙肝病毒具有逆转录酶，这是逆转录病毒独有的聚合酶。据估计，每年每个站点的乙肝病毒替换率约为10^-5。以人类T细胞白血病病毒I型和II型(HTLV-I/II)为例，我们认为其替换率远高于真核基因，但低于逆转录病毒，并利用核苷酸替换数构建了上述病毒的系统发育树。因此，我们得出的结论是，在这项研究中检查的病毒显示出“非宿主进化”。

The aim of this research project was to clarify the evolutionary features of RNA viruses from the viewpoint of molecular evolution. In particular, we studied the rate of nucleotide substitutions of RNA viruses such as human immunodeficiency viruses (HIV) and oncoviruses. We found that the substitution rates of these typical retroviruses are the order of 10^<-3> per site per year. These rates are 10^6 times greater than those of eukaryotic genes including nuclear and mitochondrial genes. Although human hepatitis B virus (HBV) is not a RNA virus, we also examined the rate of nucleotide substitution of HBV. This is because HBV possesses reverse transcriptase that is a polymerase unique to retroviruses. The substitution rate of HBV is estimated to be the order of 10^<-5> per site per year. In the case of human T cell leukemia viruses types I and II (HTLV - I / II), we suggested that the substitution rate is much higher than those of eukaryotic genes but lower than those of retroviruses.Using the numbers of nucleotide substitutions, we constructed the phylogenetic trees for the above-mentioned viruses. As the result, we concluded that the viruses examined in this research show "host-independent evolution."