Abstract
Proteolytic processing of foamy virus Gag proteins appears to be different from that of other retroviruses. A single carboxy-terminal cleavage site is consistently detectable in human foamy virus (HFV) Gag precursor protein p74Gagderived from infected cells and/or purified virus particles. Using a recombinant HFV protease, we have determined the p74Gagcleavage site that results in p70Gagand the carboxy-terminal p3Gag(Pfrepperet al.,1997,Biochem. Biophys. Res. Commun.237, 548–553). To study the biological functions of p3Gag, proviral DNA clones were constructed coding for a carboxy-terminally truncated p70Gaglacking the entire p3Gagprotein. Removal of p3Gagresulted in an about 100-fold lower virus titer. The expression of other HFV proteins and the processing of Pol proteins were indistinguishable from those of wild-type-transfected cells. The defect in viral infectivity of the p3 mutants was partially restored by coexpressing the full-length p74Gagproteinin trans.The deletion of p3Gagresulted in particle assembly with wild-type virion morphology and encapsidation of Pol proteins. Our data show that the carboxy-terminal p3Gagprotein has an important function for viral infectivity but is not required for preassembly of capsids, virus morphogenesis, and incorporation of Pol proteins into virions.
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