Rac1 exists in inactive state in the cytosol until the reception of extracellular signals by the cell. To be functional Rac1 is rapidly targeted to the plasma membrane upon cell stimulation. The main factors involved in this mobilisation are the Rac GEFs like VAV and phospholipids (PtdIns(4,5)P2, PtdIns(3,4,5) P3) and lipid rafts at the plasma membrane. VAV catalyses the disassociation of GDP from Rac1 by modifying the nucleotide-binding site such that GDP is released and subsequently replaced. The incoming GTP occupies the nucleotide binding site and finally displaces VAV from Rac1 (Bos et al. 2007, Bustelo et al. 2012).