IDENTIFICATION OF DOMAINS IN THE SIMIAN IMMUNODEFICIENCY VIRUS MATRIXPROTEIN ESSENTIAL FOR ASSEMBLY AND ENVELOPE GLYCOPROTEIN INCORPORATION

The matrix domain (MA) of the simian immunodeficiency virus (SIV) is e ncoded by the amino-terminal region of the Gag polyprotein precursor a nd is the component of the viral capsid that lines the inner surface o f the virus envelope. To define domains of the SIV MA protein that are involved in virus morphogenesis, deletion and substitution mutations were introduced in this protein in the context of a gag-protease const ruct and expressed in the vaccinia virus vector system. The MA mutants were characterized with respect to synthesis and processing of the Ga g precursor, assembly and release of virus-like particles, and incorpo ration of the envelope (Env) glycoprotein into particles, We have iden tified two regions of the SIV MA which are critical for particle forma tion. Both domains are located in a central hydrophobic ex-helix of th e SIV MA, according to data on the structure of this protein. In addit ion, we have characterized a domain whose mutation impairs the incorpo ration of SIV Env glycoproteins with long transmembrane cytoplasmic ta ils into particles. Interestingly, these mutant particles retained the ability to associate,vith SIV Env proteins with short cytoplasmic tai ls.