Further studies on the glycosylated gag gene products of Rauscher murine leukemia virus: identification of an N-terminal 45,000-dalton cleavage product.

A glycosylated 45,000-Mr protein containing Rauscher murine leukemia virus p15 and p12 antigenic sites and tryptic peptides was identified in Rauscher murine leukemia virus-infected cells. This glycoprotein, termed gP45gag, was also shown to contain a single tryptic peptide also present in gPr80gag and its unglycosylated apoprotein precursor Pr75gag, but lacking in Pr65gag or Pr40gag. The presence of this peptide only in viral precursor proteins containing the so-called leader (L) sequence strongly suggests that gPr45gag is an N-terminal fragment of larger glycosylated gag polyproteins, composed of L sequences in addition to p15 and p12. The kinetics of appearance of radiolabeled gPr45gag and its disappearance during chase-incubation is suggestive of a precursor-like role for this intermediate gene product. An observed 27,000-Mr glycosylated polypeptide, termed gP27gag and containing p15 but not p12, p30, or p10 antigenic determinants, is a candidate cleavage product derived from gPr45gag. These observations suggest that gPr45gag and its putative cleavage product gP27gag represent an authentic pathway for intracellular processing of glycosylated core proteins.