FAK and paxillin immunoprecipitate with β1 integrin following cell attachment to type IV collagen. SCC25 cells were plated in semisolid media (susp), on tissue culture plastic (pl), or on type IV collagen (col) for 2 hours. Some cultures were preincubated with antibodies which block attachment by β1 or β4 integrin subunits. β1 integrin was immunoprecipitated (IP β1) from cell lysates and western blotted using the antibodies indicated at left. These experiments were performed three times with similar results. Representative blots are shown. (B) Densitometric quantitation of blots in Fig. 1A.