Molecular evolution and phylogeny of the human AIDS viruses LAV, HTLV-III, and ARV

A phylogenetic tree for the human lymphadenopathy-associated virus (LAV), the human T-cell lymphotrophic virus type III (HTLV-III), and the acquired immune deficiency syndrome (AIDS)-associated retrovirus (ARV) has been constructed from comparisons of the amino acid sequences of their gag proteins. A method is proposed for estimating the divergence times among these AIDS viruses and the rates of nucleotide substitution for their RNA genomes. The analysis indicates that the LAV and HTLV-III strains diverged from one another after 1977 and that their common ancestor diverged from the ARV virus no more than 10 years earlier. Hence, the evolutionary diversity among strains of the AIDS viruses apparently has been generated within the last 20 years. It is estimated that the genome of the AIDS virus has a nucleotide substitution rate on the order of 10(-3) per site per year, with the rate in the second half of the genome being double that in the first half.