Functions as a RAC1 guanine nucleotide exchange factor (GEF), activating Rac proteins by exchanging bound GDP for free GTP. Its activity is synergistically activated by phosphatidylinositol 3,4,5-trisphosphate and the beta gamma subunits of heterotrimeric G protein. Mediates the activation of RAC1 in a PI3K-dependent manner. May be an important mediator of Rac signaling, acting directly downstream of both G protein-coupled receptors and phosphoinositide 3-kinase (By similarity). Interacts with RAC1. PH domain confers substrate specificity and recognition. Able to discriminate between RAC1, RHOA, and CDC42 (By similarity). DH domain alone was unable to confer substrate specificity and recognition.