Promotes the exchange of Ras-bound GDP by GTP. Probably by promoting Ras activation, regulates phosphorylation of MAP kinase MAPK3 in response to EGF (By similarity). Catalytic component of a trimeric complex that participates in transduction of signals from Ras to Rac by promoting the Rac-specific guanine nucleotide exchange factor (GEF) activity (PubMed:10499589, PubMed:11524436). Interacts (via C-terminus) with GRB2 (via SH3 domain). Forms a complex with phosphorylated MUC1 and GRB2 (via its SH3 domains). Interacts with phosphorylated LAT2. Interacts with NCK1 and NCK2 (By similarity). Part of a complex consisting of ABI1, EPS8 and SOS1 (PubMed:10499589, PubMed:11524436). Interacts (Ser-1120 and Ser-1147 phosphorylated form) with YWHAB and YWHAE (By similarity). Expressed in most embryonic and adult tissues. Phosphorylation at Ser-1120 and Ser-1147 by RPS6KA3 create YWHAB and YWHAE binding sites and which contribute to the negative regulation of EGF-induced MAPK1/3 phosphorylation.