POLYOMAVIRUS MIDDLE-T ANTIGEN ASSOCIATES WITH THE KINASE DOMAIN OF SRC-RELATED TYROSINE KINASES

Middle-T antigen of mouse polyomavirus, an oncogenic DNA virus, associ ates with and activates the cellular tyrosine kinases c-Src, c-Yes, an d Fyn. This interaction is essential for polyomavirus-mediated transfo rmation of cells in culture and tumor formation in animals, To determi ne the domain of c-Src directing association with middle-T, mutant c-S rc proteins lacking either the amino-terminal unique domain and the my ristylation signal, the SH2 domain, the SH3 domain, or all three of th ese domains were coexpressed with middle-T in NIH 3T3 cells. All mutan ts were found to associate with middle-T, demonstrating that the kinas e domain of c-Src, including the carboxy-terminal regulatory tail, is sufficient for association with middle-T. Moreover,,ve found that Hck, another member of the Src kinase family, does not bind middle-T, whil e chimeric kinases consisting of the amino-terminal domains of c-Src f used to the kinase domain of Hck or the amino-terminal domains of Hck fused to the kinase domain of c-Src associated with middle-T. Hck muta ted at its carboxy-terminal regulatory residue, tyrosine 501, was also found to associate with middle-T. These results suggest that in Hck, the postulated intramolecular interaction between the carboxy-terminal regulatory tyrosine and the SH2 domain prevents association with midd le-T, This intramolecular interaction apparently also limits the abili ty of c-Src to associate with middle-T, since removal of the SH2 or SH 3 domain increases the efficiency,vith which middle-T binds c-Src.