INCORPORATION OF HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1 GAG PROTEINS INTO MURINE LEUKEMIA-VIRUS VIRIONS

The retroviral Gag polyprotein is necessary and sufficient for assembl y and budding of viral particles. However, the exact inter- and intram olecular interactions of the Gag polyproteins during this process are not known. To locate functional domains within Gag, we generated chime ric proviruses between human immunodeficiency virus type 1 (HIV-1) and murine leukemia virus (MuLV). In these chimeric proviruses, the matri x or capsid proteins of MuLV were precisely replaced with the matrix o r capsid proteins of HIV-1. Although the chimeric proviruses were unab le to efficiently assemble into mature viral particles by themselves, coexpression of wild-type MuLV Gag rescued the HIV proteins into virio ns. The specificity of the rescue of HIV proteins into MuLV virions sh ows that specific interactions involving homologous matrix or capsid r egions of Gag are necessary for retroviral particle formation.