Has E3 ubiquitin-protein ligase activity. S-ubiquitinyl-[E2 ubiquitin-conjugating enzyme]-L-cysteine + [acceptor protein]-L-lysine = [E2 ubiquitin-conjugating enzyme]-L-cysteine + N(6)-ubiquitinyl-[acceptor protein]-L-lysine. Protein modification; protein ubiquitination. Interacts (via SH3 domain 3) with PAK2 (PubMed:16374509). Interacts with RAC1 (GTP-bound form) (PubMed:20696164). The RING finger domain is required for ubiquitin ligase activity and autoubiquitination. Autoubiquitinated. Belongs to the SH3RF family.