Analysis of p60v-src mutants carrying lesions involved in temperature sensitivity

Analysis of the src genes of three temperature-sensitive (ts) mutants of Rous sarcoma virus (tsNY68, tsNY72-4, and PA104) showed that each has two C-terminal mutations in the kinase domain required for temperature sensitivity, as assayed by morphological alteration and anchorage-independent growth. In all three mutants, one of the mutations is a valine-to-methionine change at position 461. To assess the contribution of each mutation to the biochemical properties of the src protein, we analyzed the kinase activity and the interaction with cellular proteins p50 and p90 of recombinant src gene products in which only one mutation was combined with wild-type src sequences. Chimeric src protein containing only the Met-461 mutation was indistinguishable from the wild type by all criteria examined, while the effect of the second C-terminal mutation alone varied with the defectiveness of the parental ts mutant. The second mutation alone, while not sufficient to cause ts transformation, altered p60src complex formation with cellular proteins p50 and p90 and altered the in vitro thermolability of src kinase activity. The results indicate that these biochemical properties of p60src are more sensitive to mutation than others, such as in vivo kinase activity, which require more profound structural alterations.