Analysis of two phosphoproteins related to pp60src from Schmidt-Ruppin D virus particles

During endogenous phosphorylation of partially purified pp60src from virus particles, besides pp60src two additional phosphoproteins, 45K and 42K, were found. These proteins copurify with pp60src. They were shown to be proteolytic degradation products due to the action of the virus-associated protease p15. All three phosphoproteins were present in particles of two different sarcoma virus strains, Schmidt-Ruppin D and Prague C, indicating that this phenomenon is general rather than strain-specific. The degradation rate of pp60src was reduced by the presence of 3 mM-ZnCl2, which acts as a protease inhibitor.