Fig. 6. Spectrin-containing integrin clusters form upstream of Rac activation. BAE cells were transiently transfected with plasmid encoding myc-tagged dominant-negative Rac (N17Rac). Cells were detached and replated on fibronectin for 1 hour, fixed and permeabilized. Spectrin distribution was detected with polyclonal antibodies against spectrin. Cells expressing dominant-negative Rac were detected with anti-myc antibody. Actin filaments were detected with TRITC-labeled phalloidin. Rac- and spectrin-containing clusters are indicated with arrows. Three independent fields are shown. Bar, 20 µm.