Functions as a RAC guanine nucleotide exchange factor (GEF), which activates the 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. May function downstream of heterotrimeric G proteins in neutrophils. Interacts preferentially with RAC2. Interacts with RAC1. Mainly expressed in peripheral blood leukocytes and brain. Expressed at intermediate level in spleen and lymph nodes, and weakly expressed in other tissues. 3 isoforms of the human protein are produced by alternative splicing. Note: This description may include information from UniProtKB.