Guanine nucleotide exchange factor for Arf GTPases, stimulating the nucleotide exchange from the GDP-bound to the GTP-bound form. Catalyzes both the GDP release by and the GTP binding to ARF2. Has no exchange activity on Rab GTPases. Involved in vesicular transport. Inhibited by brefeldin A. The SEC7 domain is sufficient for nucleotide exchange activity. Present with 279 molecules/cell in log phase SD medium.