Biochemical and immunological characterization of the major structural proteins of feline immunodeficiency virus

Feline immunodeficiency virus (FIV) structural proteins were identified using sera obtained from experimentally inoculated cats. Proteins analysed by both radioimmunoprecipitation and Western blotting were specific for FIV infection and failed to cross-react with either antisera to feline leukaemia virus of feline syncytium-forming virus. Western blot analysis of purified virus revealed immunoreactive proteins with apparent Mr of 65K, 50K, 40K, 32K, 24K, 15K and 10K. The major core structural proteins of the virus were isolated by reverse phase HPLC and the aminoterminal sequences of p10 and p24 were determined. Monoclonal antibodies specific for p24 suggested the presence of a precursor protein that could be detected in 35[S]methionine/cysteine-labelled, virus-infected cell extracts. This putative precursor protein possessed an apparent Mr of 50K (Pr50gag). Further analysis revealed the presence of two additional proteins of 130K and 40K. Experiments utilizing tunicamycin, endoglycosidase H and glycopeptidase F revealed that p130 and p40 exhibited properties characteristic of glycoproteins. Our studies also indicated that FIV is immunologically related to other lentiviruses.