Physicochemical Characterization and Specificity of the Murine Leukaemia Virus Pr65gag Proteolytic Factor

Abstract

The Pr65gag proteolytic factor obtained from Moloney or Rauscher leukemia virus was characterized. It was present in small amounts in virions and was extremely unstable. Although it eluted at the trailing edge of p12 on Sephadex G-75 columns, it could clearly be separated from p12 on DEA-Sephadex A-50M columns, making it unlikely that the factor is p12 or any other major murine leukemia virus (MuLV) protein. This facto also distinguishes the murine factor from the avian p15-associated protease which is present in large amounts in avian tumor viruses and is stable to column purification methods. The murine proteolytic factor had an estimated MW of 20,000-22,000, relative to MuLV p12, which eluted as a dimer on Sephadex G-75 columns in the presence of 0.1% NP-40. In vitro cleavage of an iodinated Pr65gag-rich, p30-deficient substrate yielded a clear increase in p30 and p12, which suggests that the in vitro cleavage of Pr65gag is similar to its processing in vivo.