Maturation of murine leukemia virus env proteins in the absence of other viral proteins.

A mutant of Akv which produces env but no detectable gag or pol products (A. Rein, D. R. Lowy, B. I. Gerwin, S. K. Ruscetti, and R. H. Bassin, J. Virol. 41, 626-634 (1982] was examined for maturation of env gene protein products. In comparison with wild-type Akv, the mutant AK 71 synthesizes gPr85env and produces gp70 and Prp15E in normal amounts and with normal kinetics. Cell surface gp70 was found alike in the mutant and wild type. However, cleavage of Pr15E to p15E did not occur in the mutant. This final cleavage step of AK 71 Prp15E could be made to occur by superinfecting cells containing the mutant with baboon endogenous virus. Thus, unlike earlier steps, this final step in maturation of the env gene product appears to require gag or pol gene products. It is proposed that the virus-encoded protease is required for this last step.