Analysis of the envelope region of the highly divergent HIV-2ALT isolate extends the known range of variability within the primate immunodeficiency viruses.

HIV-2ALT is a highly divergent HIV-2-related isolate that is genetically equidistant to the prototypic HIV-2 strains, defined by HIV-2ROD, and to the simian immunodeficiency viruses SIVmac and SIVsm. We have now cloned and sequenced the envelope region of HIV-2ALT, thus completing the analysis of the whole viral genome. The sequences of env and nef and of the second exons of tat and rev were compared with those of the other viruses of the HIV-2/SIVsm/SIVmac group. Despite of the high degree of variation of HIV-2ALT, functional domains of the genes are conserved. Although in env, the overall pattern of constant and variable domains is maintained, many single amino acid exchanges exist at positions previously thought to be constant in HIV-2 strains. In addition, when compared with a broader spectrum of immunodeficiency viruses, which includes SIVMND from mandrill and SIVAGM from African green monkey, HIV-2ALT Env has a high percentage of amino acid exchanges, which are unique to this strain. This underlines the separate branch of HIV-2ALT within the phylogenetic tree and makes obvious the inclusion of such divergent strains in preventive and therapeutic programs.