“…It is well known that many viral tyrosine kinases (e.g., pp6Ov-src) localize to FACs in transformed cells (Cooper and Hunter, 1981;Kellie et al, 1986a,b;Tapley et al, 1989;Turner et al, 1989;Guan and Shalloway, 1992;Lipfert et al, 1992) and that phosphotyrosine (PTyr)-containing proteins localize to FACs within normal cells (Marchisio et al, 1984;Maher et al, 1985). Furthermore, one integrin-associated focal adhesion kinase, pp125FAK, exhibits both growth factor and ECM-dependent phosphorylation on tyrosine (Guan et al, 1991;Kornberg et al, 1992;Zachary and Rozengurt, 1992) and physically associates with pp6Oc-src via its SH2 domain when activated Xing et al, 1994;Cobb et al, 1994). pp125FAK is a substrate for pp6Ov-src, along with many other FAC proteins (Rohrschneider et al, 1982;Kellie et al, 1986b;Tapley et al, 1989;Guan and Shalloway, 1992) and a recent report suggests that integrin-dependent phosphorylation of pp125FAK may link integrin engagement to the Ras/MAP kinase signal transduction pathway via creation of an SH2-binding site for GRB2 (Schlaepfer et al, 1994). The distribution of ppl25FAK within FACs as well as its ability to be activated by growth factors appears, however, to be more dependent on its associations with the actin CSK (Lipfert et al, 1992;Rankin and Rozengurt, 1994).…”