Identification of tryptic peptides unique to a 110,000-molecular weight polyprotein encoded by the T-8 isolate of murine leukemia virus.

Abstract

Mink cells nonproductively-infected with the weakly-transforming T-8 isolate of murine leukemia virus (MuLV) express a 110,000 mol wt polyprotein designated T-8 P110. By immunoprecipitation analysis, T-8 P110 is shown to contain AKR-MuLV amino terminal gag gene-specific components (p15, p12) but to lack p30, p10, gp70, and p15(E) antigenic determinants. These observations are further substantiated by tryptic peptide analysis indicating T-8 P110 to share approximately six lysine-containing tryptic peptides with AKR-MuLV Pr65gag, and none with AKr-MuLV Pr82env. Furthermore, of seven methionine-containing T-8 P110 tryptic peptides, at least four can be conclusively shown not to be present in either AKr-MuLV Pr180gag/pol or Pr82env. A clonal mink cell line nonproductively infected by T-8, and expressing high levels of P110, although not morphologically transformed, is shown to lack elevated levels of tyrosine-specific protein kinase activity and reduction of epidermal growth factor binding sites characteristic of cells transformed by many other RNA-transforming viruses. These findings argue either that the T-8 viral genome contains acquired cellular sequences encoding a portion of P110, or that T-8 P110 represents an inphase deletion of AKR-MuLV Pr180gag/pol with extensive posttranlational modification and that an as yet unidentified protein is responsible for T-8 associated transformation.

Identification of a 36,000-molecular weight, gag-related phosphoprotein in lymphoma cells transformed by radiation leukemia virus.

“…Unlike AbLV p120, p36 was not found to contain phosphotyrosine and did not show any detectable ATP-specific protein kinase activity. However, these findings were not unexpected, as the phosphorylation of tyrosine has not been found associated with tumorigenesis by MuLV; additionally several other defined onc gene products, including those of the murine sarcoma viruses (35,36), do not possess any ATP-specific protein kinase function.…”