INCORPORATION OF HOMOLOGOUS AND HETEROLOGOUS PROTEINS INTO THE ENVELOPE OF MOLONEY MURINE LEUKEMIA-VIRUS

The efficiencies with which homologous and heterologous proteins are i ncorporated into the envelope of Moloney murine leukemia virus (M-MuLV ) have been analyzed by utilizing a heterologous, Semliki Forest virus -driven M-MuLV assembly system and quantitative pulse-chase assays. Ho mologous M-MuLV spike protein was found to be efficiently incorporated into extracellular virus particles when expressed at a relatively low density at the plasma membrane. In contrast, efficient incorporation of heterologous proteins (the spike complex of Semliki Forest virus an d a cytoplasmically truncated mutant of the human transferrin receptor ) was observed only when these proteins were expressed at high densiti es at the cell surface. These results imply that homologous and hetero logous proteins are incorporated into the M-MuLV envelope via two dist inct pathways.