Synthesis and processing of precursor polypeptides to murine mammary tumor virus structural proteins

Biosynthesis of murine mammary tumor virus (MuMTV) proteins was studied in the chronically MuMTV-infected epithelial cell line MuMT- 73 by using monospecific antisera to the major MuMTV core protein p27 and the major envelope glycoprotein gp47. In pulse-labeling experiments using [³⁵S]methionine, monospecific antisera to p27 precipitated a 75,000-molecular-weight protein as the major intracellular component. Analysis of the same cellular extracts with monospecific antisera to gp47 revealed that the gp47 precursor was a 70,000-dalton protein. After chase periods, there was a loss of label from the precursors and a concomitant increase of labeled extracellular mature viral proteins. The glycoprotein precursor incorporated labeled glucosamine and seemed to be processed more rapidly than the p27 precursor. Considerable amounts of apparently nonvirion-associated gp47 and glycoprotein precursor could be detected in the extracellular culture fluid.