Moloney MSV temperature sensitive transformation mutants have been isolated which exhibit coordinate temperature sensitive expression of several transformation parameters. Genetic and biochemical studies of one of these isolates, ts110, and several spontaneous wild type revertants are in progress. The ts MSV genome has been transferred to normal mouse cells by DNA transfection using high molecular weight DNA from temperature sensitive transformed rat cells. MSV pseudotypes rescued from ts110 transformed rat cells contain a heat labile low molecular weight protein kinase. This represents the only instance reported to date where a murine sarcoma virus transformation defect can be correlated with a specific enzymatic defect.