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 .
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 .
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 .
Subcellular locations: Cytoplasm, Cytosol, Endoplasmic reticulum, Mitochondrion, Nucleus
Nuclear import is dependent on complexing with a GTPase containing a C-terminal polybasic region.