A. The Tiam1/BcrGEF/GAP complex regulates Rac1 activity.
B. Coupled GEF/GAP complexes tightly regulate Rho-GTPase activity by increasing the effective GTPase “off” rate and/or by reducing signal spread.
C. GEF/GAP complexes may toggle between associated and dissociated states to achieve the observed cellular patterns of GTPase activation.
D. Rho-family GEFs and GAPs are large, multidomain proteins that can scaffold functional protein complexes. Different GEF/GAP complexes could assemble different signaling modules, adding complexity and flexibility to Rho-GTPase signaling.