Has E3 ubiquitin-protein ligase activity. In the absence of an external substrate, it can catalyze self-ubiquitination. Stimulates ubiquitination of potassium channel KCNJ1, enhancing its dynamin-dependent and clathrin-independent endocytosis (By similarity). Acts as a scaffold protein that coordinates with MAPK8IP1/JIP1 in organizing different components of the JNK pathway, including RAC1 or RAC2, MAP3K11/MLK3 or MAP3K7/TAK1, MAP2K7/MKK7, MAPK8/JNK1 and/or MAPK9/JNK2 into a functional multiprotein complex to ensure the effective activation of the JNK signaling pathway. Regulates the differentiation of CD4(+) and CD8(+) T-cells and promotes T-helper 1 (Th1) cell differentiation. Regulates the activation of MAPK8/JNK1 and MAPK9/JNK2 in CD4(+) T-cells and the activation of MAPK8/JNK1 in CD8(+) T-cells (PubMed:23963642, PubMed:27084103, PubMed:9482736). Plays a crucial role in the migration of neocortical neurons in the developing brain. Controls proper cortical neuronal migration and the formation of proximal cytoplasmic dilation in the leading process (PCDLP) in migratory neocortical neurons by regulating the proper localization of activated RAC1 and F-actin assembly (PubMed:22959435). 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 with HERP1 (By similarity). Interacts with RAC1; in a GTP-dependent manner (PubMed:22959435, PubMed:9482736). Interacts with MAP3K10/MLK2 and MAP3K11/MLK3. Interacts with MAPK8IP; this interaction leads to the PJAC complex (POSH-JIP or SH3RF1/MAPK8IP1 apoptotic complex) with a 1:1 ratio. Interacts with SIAH1. Probably part of a signaling complex that may contain SH3RF1, MAPK8IP, DLK1, MAP2K4/MKK4, MAP2K7/MKK7, MAPK8/JNK1, MAPK9/JNK2, AKT1 and AKT2 (PubMed:12514131, PubMed:14504284, PubMed:16230351, PubMed:16571722, PubMed:23963642). Found in a complex with RAC2, MAP3K7/TAK1, MAP2K7/MKK7, MAPK8IP1/JIP1, MAPK8/JNK1 and MAPK9/JNK2 (PubMed:27084103). Found in a complex with RAC1, MAP3K11/MLK3, MAP2K7/MKK7, MAPK8IP1/JIP1 and MAPK8/JNK1 (PubMed:23963642). Interacts with SH3RF2 (By similarity). Colocalizes, with AKT2 in lamellipodia. Colocalizes, with HERP1, in trans-Golgi network (By similarity). Ubiquitously expressed. Expressed in the embryonic brain. Expressed strongly in the venricular zone (VZ), subventricular zone (SVZ), and lower intermediate zone (IZ) but weakly in the upper IZ and cortical plate (CP) at 14.5 dpc. At 16.5 dpc, expression increases in the IZ and CP. At 18.5 dpc, it increases significantly in the CP but decreases in the IZ, SVZ, and VZ (at protein level). The RING finger domain is required for ubiquitin ligase activity and autoubiquitination. Phosphorylated at Ser-304 by AKT1 and AKT2. When phosphorylated, it has reduced ability to bind Rac. Autoubiquitinated. Ubiquitinated by SH3RF2, leading to proteasome-mediated degradation. Belongs to the SH3RF family.