Promotes the exchange of Ras-bound GDP by GTP (PubMed:8493579). Probably by promoting Ras activation, regulates phosphorylation of MAP kinase MAPK3 in response to EGF (PubMed:17339331). 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 (By similarity). Interacts (via C-terminus) with GRB2 (via SH3 domain) (PubMed:8493579, PubMed:7664271). Forms a complex with phosphorylated MUC1 and GRB2 (via its SH3 domains) (PubMed:7664271). Interacts with phosphorylated LAT2 (PubMed:12486104). Interacts with NCK1 and NCK2 (PubMed:10026169). Part of a complex consisting of ABI1, EPS8 and SOS1 (By similarity). Interacts (Ser-1134 and Ser-1161 phosphorylated form) with YWHAB and YWHAE (PubMed:22827337). Expressed in gingival tissues. Phosphorylation at Ser-1134 and Ser-1161 by RPS6KA3 create YWHAB and YWHAE binding sites and which contribute to the negative regulation of EGF-induced MAPK1/3 phosphorylation. The disease is caused by variants affecting the gene represented in this entry. The disease is caused by variants affecting the gene represented in this entry. Son of sevenless entry