Expression of the v-mos gene alters a M(r) 55,000 protein during acute infection by Moloney murine sarcoma virus

Infection of the rat myoblast cell line, L₆E₉, with Moloney murine sarcoma virus (Mo-MuSV) clone 124, altered a cellular protein of M(r) 55,000 (P55) within 2 days of infection. The alteration of P55 was observed as a reduction in its steady-state level in cell extracts. The reduction of P55 correlated with the appearance of p37(mos) in infected cells. Except for P55 and one other protein, no change was detected in the total protein pattern of infection cells compared to uninfected cells, as judged by either immunoblots of one-dimensional NaDodSO₄ gels or direct two-dimensional gel analysis. P55 levels were unchanged when L₆E₉ cells were infected with Moloney murine leukemia virus or several different transforming retroviruses. To determine the specificity of this v-mos-induced effect on P55, L₆E₉ cells were acutely infected with a temperature-sensitive variant (ts110) of Mo-MuSV. When these cells were shifted from 39°C to 33°C, which activates the gag-mos gene product, the P55 level dropped by >50% within 2-3 hr. Conversely, with a shift in temperature from 33°C to 39°C, the cells' P55 level returned to normal within 5 hr, starting at 30 min after shift. These results clearly show that v-mos expression in acutely infected L₆E₉ cells alters the cellular protein, P55.