Temperature Sensitive Phosphoproteins in Rat Cells Transformed by a Temperature Sensitive Mutant of Rous Sarcoma Virus

Abstract

The localization of the src-encoded protein kinase was examined by fractionating cellular extracts from rat cells transformed by a wild type and a temperature-sensitive mutant of Rous sarcoma virus (SR-A 3 Y 1 and ts 68 3 Y 1 cells). It was found to be specifically localized in the post-microsomal supernatant (PMS) fraction. Furthermore, it was noticed that a protein with a molecular weight of 16, 000 (16 K-protein) in the PMS fraction was phosphorylated in vitro when the PMS fraction from ts 68 3 Y 1 cells was preincubated at 33°C, but not at 42°C. This protein was phosphorylated when the fraction from SR-A 3 Y 1 cells was preincubated at 33°C and at 42°C. Similar temperature-sensitive phosphorylation of 16 K-protein was also observed in the PMS fraction from ts 68 3 Y 1 cells labeled in vivo with [³²P]-orthophosphate at 33°C. These results suggest that this 16 K-protein might be a candidate for the endogenous acceptor for the src-encoded protein kinase.