Molecular evolutionary study of RNA viral genes.

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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."