Selective effect of Rous sarcoma virus src gene expression on contractile protein synthesis in chick embryo myotubes

Myogenic precursor cells were infected with a temperature-sensitive mutant of Rous sarcoma virus and maintained at the permissive temperature for transformation. Following subculture, a population of cells was produced which failed to differentiate at the permissive temperature but produced a high proportion of myotubes in sister cultures shifted to the nonpermissive temperature. The myotube-containing cultures were further enriched for this cell type by the addition of 1-beta-D-arabinofuranosylcytosine to kill replicating mononucleated cells. This myotube population was suitable for testing the effect of viral-transforming gene expression in a postmitotic, terminally differentiated cell which expresses relatively low levels of the cellular homologue of the viral-transforming gene and is resistant to infection by the virus. The consequence of shifting these Rous sarcoma virus-infected myotube cultures to the permissive temperature was assessed in terms of protein synthesis. The total rate of incorporation of exogenous radioactive leucine, supplied at a concentration which saturated the intracellular pool, was similar between cultures held at the two temperatures, suggesting that the absolute rate of total protein synthesis was not affected by expression of viral-transforming gene. In contrast, the rate of synthesis of eight proteins the expression of which is specific for myotubes was suppressed reversibly. The rate of synthesis of five other proteins which are not selectively concentrated in myotubes was either unaffected or stimulated. Thus. the expression of viral-transforming gene in myotubes leads to differential effects on developmentally regulated proteins without inducing several properties of the transformed state classically observed for fibroblastic cells.