Cercopithecus aethiops (African Green monkey), a nonhuman primate species distributed throughout subsaharan Africa, has been shown to have high seroprevalence rates of antibodies to simian immunodeficiency virus (SIV), and therefore, has been proposed as a natural reservoir for immunodeficiency viruses. Our laboratories have isolated SIV-like viruses from two East African subspecies of C. aethiops designated grivet and vervet monkeys. Analysis of the structural proteins based on the molecular weights and immunologic cross-reactivity to the prototypic SIVMAC, HIV-1, and HIV-2 isolates suggests that these viruses are distinctly different. Heterogeneity was observed in the molecular weights of the gag, pol, and env gene products between SIV isolates from vervets [SIVAGM(VER)] and grivets [SIVAGM(GRI)]. Phenotypically, SIVAGM(VER) isolates were distinguishable from SIVAGM(GRI) isolates by the apparent size difference of the major core antigen p24. All SIVAGM(GRI) and SIVAGM(VER) isolates were found to encode a transmembrane protein of approximately 40 kD (gp40) in contrast to gp32 of SIVMAC. Furthermore, the transmembrane protein was shown to be encoded by the entire env open reading frame, unlike gp32 of SICMAC or gp36 of SIVAGM(TYO-1). These data indicate that viruses from C. aethiops share common features with SIVMAC and HIV-1, but represent diverse SIV-like viruses which may vary according to subspecies and geographic location.
