Gag-mos Polyproteins encoded by variants of the Moloney strain of mouse sarcoma virus

Two revertants of ts110 Moloney murine sarcoma virus (MuSV) with wild-type MuSV phenotype were examined for the presence of mos gene products, ts110 MuSV has a temperature-sensitive defect in a function required to maintain the transformed phenotype. The nonproducer 6m2 cell clone transformed by ts110 produces an 85,000-Da gag-mos protein (P85gag-mos) and a 58,000-Da gag protein (P58gag). A spontaneous revertant (clone 54-5A4) of the 6m2 cell clone produces a 100,000-Da protein (P100) recognized by antisera raised against murine leukemia virus p15, p12, and p30 but lacks determinants of p10, reverse transcriptase, and gp70. P100 was specifically recognized by antisera (anti-C3) prepared against a synthetic peptide representing the predicted C-terminal 12 amino acids of Moloney MuSV v-mos gene. Normal sera or anti-C3 blocked with excess synthetic peptide did not recognize P100. Thus, P100 is a product of the gag and mos genes. P100 was found to be phosphorylated. A second wild-type revertant (clone 204-3) was obtained by superinfection of ts110 nonproducer cells with Simian sarcoma associated virus (SSAV); it was also found to contain a phosphorylated P100gag-mos protein. The 204-3 cell clone also contained two gag polyproteins (Pr60gag and Pr55gag) of the size and antigenic properties of those found in SSAV-infected cells. These results provide two examples of P100 gag-mos proteins both derived from the P85gag-mos producing 6m2 cell clone. The P100 gag-mos polyproteins are made in amounts that are easily detected by radiolabeling experiments using [3H]leucine. The intracellular viral RNAs present in 6m2 cells and the two revertant clones were also examined. All three cell clones contained a 4.0 kb RNA hybridizing to v-mos sequences but only the 6m2 clone contained a 3.5 kb mos-containing RNA. Our findings indicate that the 3.5 kb RNA codes for P85gag-mos in cell-free translation experiments (Junghans et al., 1982, J. Mol. Biol. 161, 229). These findings as they relate to the mechanism that produces P100gag-mos instead of P85gag-mos are discussed.