VAV exists in an auto-inhibitory state, folded in such a way as to inhibit the GEF activity of its DH domain. This folding is mediated through binding of tyrosines in the acidic domain to the DH domain and through binding of the calponin homology (CH) domain to the C1 region. Activation of VAV may involve three events which relieve this auto-inhibition: phosphorylation of tyrosines in the acidic domain causes them to be displaced from the DH domain; binding of a ligand to the CH domain may cause it to release the C1 domain; binding of the PI3K product PIP3 to the PH domain may alter its conformation (Aghazadeh et al. 2000). VAV2/3 are phosphorylated on Y172/Y173 respectively in the acidic domain. This is mediated by SYK and Src-family tyrosine kinases (Deckert et al. 1996, Schuebel et al. 1998). Once activated, VAV2/VAV3 are involved in the activation of RAC1, PAK1, MEK and ERK.