P65 of gazdar murine sarcoma viruses contains antigenic determinants from all four of the murine leukemia virus (MuLV) gag polypeptides (p15, p12, p30, and p 10) and can be cleaved in vitro by the MuLV proteolytic activity

Abstract

Thin-section electron micrographs of Gazdar murine sarcoma virus (Gz-MSV) particles showed that 100% of the particles possessed an immature morphology. Correspondingly, p65 (the major 65,000-dalton protein observed on sodium dodecyl sulfate-polyacrylamide gel electrophoresis for Gz-MSV particles) possessed antigenic determinants from all four of the murine leukemia virus (MuLV) Pr65 gag polypeptides—that is, p30, p15, p12, and p10. This result is in contrast to earlier observations ( A. Pinter and E. deHarven (1979), Virology, 99, 103–110) which reported that p65 lacked antigenic determinants of MuLV p10. It is consistent with the recent finding of Maxwell and Arlinghaus ((1981), J. Virol., 39, 963–967) that Gz-MSV p65, when cleaved in vitro, gives rise to a polypeptide with the size and antigenic determinant of MuLV p10. Thus, we suggest that Gz-MSV p65 should be designated as Gz-MSV Pr65 gag. We also found that Gz-MSV Pr65 gag could be cleaved in vitro by using a partially purified proteolytic factor that had been derived from Moloney murine leukemia virus (M-MuLV) by Sephadex G-75 column chromatography ( Y. Yoshinaka and R. B. Luftig (1980), J. Gen. Virol., 48, 329–340). Protein bands were produced that migrated on gels and had the same antigenic determinants as the MuLV intermediates Pr40 gag (p30, p10) and Pr27 gag (p15, p12). Pr55 gag (p15, p12, p30), a minor component, was also produced. Additional incubation of Gz-MSV Pr65 gag led to a breakdown of the intermediate polyproteins into the four MuLV gag polypeptides p30, p10, p15, and p12. The final processing of Pr55 gag and Pr40 gag occurred more rapidly than that of Pr27 gag. It thus seems that in vitro sequentially different processing events are involved in production of the four internal gag antigens from Gz-MSV Pr65 gag.