The expression of pp60 src and its associated protein kinase activity in cells infected with different transformation-defective temperature-sensitive mutants of rous sarcoma virus

Abstract

A set of five transformation-defective temperature-sensitive mutants of Rous sarcoma virus has been used to investigate the relation between pp60 src its associated protein kinase activity, and expression of the transformed phenotype. In radioimmune competition experiments, the levels of pp60 src induced by the mutants did not vary by more than a factor of two, either among the mutants at a given temperature or between nonpermissive and permissive temperatures for a given mutant. The mutants fell into two distinct classes with respect to the temperature conditional expression of pp60 src-associated kinase activity. Three mutants (GI 201, GI 202, and GI 251) induced two- to fivefold higher levels of pp60 src-associated kinase activity at the permissive temperature. The other mutants GI 203 and 253 induced only very low levels of pp60 src-associated kinase at either temperature. The pp60 src-associated kinase activity induced by GI 201, 202, and 251 at the permissive temperature was significantly more heat labile in vitro than that of the wild type. Furthermore, downshift of the mutant-infected cells to the permissive temperature resulted in a rapid increase (within 15 min) in the pp60 src-associated kinase activity only with mutants GI 201, GI 202, and GI 251, i.e., only with those mutants having an elevated activity at the permissive temperature. The results taken as a whole suggest that there is not a simple relationship between pp60 src, pp60 src-associated kinase activity, and transformation and support the idea of multifunctionality of the src gene product.