Immunoprecipitation with FAK and paxillin antibodies removes major phosphorylated bands from stromal cell, but not RAMOS cell lysate. Stromal cells were incubated in medium alone (−) or with RAMOS cells (+) for 5 minutes at 37°C. Stromal cells and RAMOS cells were collected separately, lysed, and incubated with antibody-coated protein A sepharose overnight at 4°C as described in the Materials and Methods. Sepharose beads were sedimented by centrifugation for 10 seconds. The supernatant lysate was removed, electrophoresed through 10% SDS gels, and immunoblotted with antiphosphotyrosine. Lanes represent original lysate (lane 6) or supernatant lysates removed from preimmune rabbit IgG (lane 1), antipaxillin (lanes 2, 3, and 7) or anti-FAK (lanes 4, 5, and 8) immunoprecipitations. Stromal cells in contact (+) were equal protein amounts pooled from stromal cells incubated with RAMOS-wt or RAMOS-4c. RAMOS cells were equal protein amounts pooled from samples containing RAMOS-wt and RAMOS-4c. Results are representative of three individual experiments.