Definition

Acts as a GEF (guanine nucleotide exchange factor) for the Rho family of small GTP-binding proteins (G proteins) that stimulates the dissociation of GDP to enable subsequent binding of GTP. Additionally, appears to chaperone the processing and/or trafficking of small GTPases containing a C-terminal polybasic region independently of GEF activity. Targets include RAP1A/RAP1B, RHOA, RHOB, RHOC, RAC1 and KRAS. Regulates mitochondrial dynamics by controlling RHOT function to promote mitochondrial fission during high calcium conditions. Able to promote the Ca(2+) release from the endoplasmic reticulum via both inositol trisphosphate (Ins3P) and ryanodine sensitive receptors leading to a enhanced mitochondrial Ca(2+) uptake.; [Isoform 1]: Acts as a GEF (guanine nucleotide exchange factor) for unprenylated RHOA. Chaperones the entry and passage of small GTPases through the prenylation pathway. Recognizes the last amino acid in the GTPase C-terminal CAAX motif with a preference for 'Leu' over 'Met', indicating involvement in the geranylgeranylation pathway.; [Isoform 2]: Acts as a GEF (guanine nucleotide exchange factor) for prenylated RHOA. Acts as a GEF for RHOC. Chaperones the downstream trafficking and/or processing of small newly prenylated GTPases. Escorts RAC1 to the nucleus.