Point mutations in Moloney murine leukemia virus envelope protein: effects on infectivity, virion association, and superinfection resistance.

Retroviral envelope proteins are synthesized in the infected cell and targetted to the assembling virion; during infection, they mediate receptor binding and fusion of the virion and cell membranes. We have generated a series of mutants of the Moloney murine leukemia virus (M-MuLV) with alterations in the TM protein, p15E, and determined whether the mutants are defective for replication and where the defects lie. Twenty-one point mutants were assessed for infectivity, virion-associated envelope protein levels, and the ability to confer resistance to superinfection. Only one mutant was specifically defective in a post-receptor binding step. Three other mutants encoded virion-associated envelope proteins that could not confer resistance to superinfection, implying that they could not bind to the receptor. These mutants demonstrate that in M-MuLV, receptor binding and early events such as membrane fusion can be affected by amino acid changes in the TM protein.