p56lck stably associates with a 115 kDa substrate.

Using antibodies directed against p56lck, we have identified a 115 kDa protein (p115) that is specifically immunoprecipitated with p56lck from whole cell lysates. The p56lck/p115 complex is stable in the presence of nonionic detergents. p115 becomes phosphorylated on tyrosine residues in p56lck immune-complex kinase assays. Treatment of whole cells with 12-O-tetradecanoyl phorbol-13-acetate decreases the subsequent tyrosine phosphorylation of p115 in immune-complex kinase assays.