Cellular signaling by G-proteins is down-regulated by GTPase-activating proteins (GAPs), which increase the rate of GTP hydroylsis. The GTPase regulator associated with focal adhesion kinase (GRAF) has GAP activity toward Rho A and Cdc42, but not Rac1. GRAF is ubiquitously expressed with high levels in heart and brain. Expression of GRAF causes clearing of stress fibers and formation of long actin based filopodial-like extensions. Fusion of MLL with GRAF, MLL/GRAF, is included in a rare gene