Cleavage of Rauscher Leukaemia Virus (R-MuLV) Pr65gag by the Moloney Leukaemia Virus (M-MuLV) Proteolytic Activity Produces the R-MuLV-specific but not the M-MuLV-specific 40000 Dalton Intermediate Polypeptide

Although the Pr65^gag precursor polyproteins of Moloney murine leukaemia virus (M-MuLV) and of Rauscher murine leukaemia virus (R-MuLV) have the same apparent mol. wt. by SDS-polyacrylamide gel electrophoresis (SDS-PAGE), their initial 40000 dalton intermediate cleavage products differ in mol. wt., i.e. the M-MuLV product (Pr41.5^gag) is 1500 daltons larger than the R-MuLV product (Pr40^gag). We took advantage of this difference to show that in vitro cleavage of R-MuLV Pr65^gag by the M-MuLV proteolytic activity gives rise to R-MuLV Pr40^gag and not M-MuLV Pr41.5^gag. This result suggests that the specificity for cleavage of the MuLV Pr65^gag is built into the substrate.

^† Present address: Department of Microbiology, Mie University School of Medicine, 174 Edobashi-2-Chome, Tsu, Mie, Japan 514.