Maximum likelihood analysis of adaptive evolution in HIV-1 gp120 env gene.

Every functional protein appears to have some conserved amino acids which are critically important to the basic structure and function of the protein and thus under purifying selection. Some proteins also have variable amino acids which, when changed, offer a selective advantage, and thus undergo adaptive evolution. These amino acids are also important to the structure and function of the protein, although in a different way. It seems that the selective pressure in every protein varies among sites. Maximum likelihood models developed recently for comparison of silent and replacement nucleotide substitution rates allow for variable selective pressures among amino acid sites, and provide a powerful approach to studying the evolutionary process of protein-coding genes. This paper applies the likelihood models to analyze a data set of 186 HIV-1 gp120 env gene sequences for comparison with a previous analysis of the same data set. The maximum likelihood analysis identified a number of sites under positive selection, some in the conserved regions of the protein.