In vitro phosphorylation of the 36K protein in extract from Rous sarcoma virus-transformed chicken fibroblasts.

When cell-free extracts of chickens embryo fibroblasts transformed by Rous sarcoma virus (RSV) were incubated with [gamma-32P]ATP, a protein having a Mr of 36,000 was phosphorylated. Two-dimensional electrophoresis of a mixture of phosphorylated proteins formed in vitro and in vivo showed that they are indistinguishable. The in vitro phosphorylation of the Mr = 36,000 protein was completely inhibited by serum isolated from rabbit bearing tumor formed by RSV. In addition, phosphorylation of the 36K protein does not occur if the extract was made from fibroblasts transformed by RSV tsNY68 and cultured at 42 degrees C or from fibroblasts infected with transformation defective RSV. The cell free-phosphorylation of 36K protein was dependent on Mg2+ ions but not dependent on exogenously added cyclic AMP.