ABL PROTEIN-TYROSINE KINASE SELECTS THE CRK ADAPTER AS A SUBSTRATE USING SH3-BINDING SITES

To understand the normal and oncogenic functions of the protein-tryosi ne kinase Abl, the yeast two-hybrid system has been used for identifyi ng proteins that interact with it. One interacting protein is Crk-I, a n SH3/SH2-containing adapter protein that was originally identified as the oncogenic element in the avian sarcoma virus CT10. Direct interac tion between the Crk-I SH3 and Abl at novel, similar to 10 amino acid sites just carboxy-terminal to the Abl kinase domain occurs in vitro a nd in mammalian cells. There is a nearby site specific for binding ano ther adapter, Nck, and these sites also bind Grb-2. When bound to Abl, Crk-I was phosphorylated on tyrosine. Thus, the SH3-binding sites on Abl serve as substrate recognition sites for the relatively nonspecifi c kinase of Abl. In Crk-I-transformed cells, Crk-I associates with end ogenous c-Abl and is phosphorylated on tyrosine. The association of Cr k and Abl suggests that Abl could play a role in v-Crk and Crk-I trans formation and that normal Abl function may be partly mediated through bound adapter molecules.