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 (PubMed:28630045, PubMed:30190425, PubMed:1549351, PubMed:11948427, PubMed:20709748). Additionally, appears to chaperone the processing and/or trafficking of small GTPases containing a C-terminal polybasic region independently of GEF activity (PubMed:20709748, PubMed:21242305). Targets include RAP1A/RAP1B, RHOA, RHOB, RHOC, RAC1 and KRAS (PubMed:1549351, PubMed:11948427, PubMed:20709748, PubMed:24415755). Regulates mitochondrial dynamics by controlling RHOT function to promote mitochondrial fission during high calcium conditions (PubMed:27716788). 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 (PubMed:24349085). Acts as a GEF (guanine nucleotide exchange factor) for unprenylated RHOA (PubMed:30190425, PubMed:28630045, PubMed:24415755). Chaperones the entry and passage of small GTPases through the prenylation pathway (PubMed:20709748). 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 (PubMed:24415755). Acts as a GEF (guanine nucleotide exchange factor) for prenylated RHOA (PubMed:28630045, PubMed:30190425, PubMed:21242305). Acts as a GEF for RHOC (PubMed:21242305). Chaperones the downstream trafficking and/or processing of small newly prenylated GTPases (PubMed:20709748). Escorts RAC1 to the nucleus (PubMed:12551911). Interacts with RABL3 (PubMed:31406347). Interacts with RHOT1 (PubMed:27716788). Interacts with unprenylated RHOA; the interaction is direct (PubMed:28630045, PubMed:30190425, PubMed:20709748). Interacts with RAP1A (PubMed:20709748). Interacts with KRAS (PubMed:20709748, PubMed:24415755). Interacts with RAC1 (PubMed:20709748). Interacts with RAP1B (PubMed:24415755). Preferentially interacts with unprenylated GTPases that will become geranylgeranylated (PubMed:24415755). May also interact with prenylated GTPases (PubMed:24415755). Interacts with prenylated RHOA; the interaction is direct and in a 1:1 stoichiometry (PubMed:28630045, PubMed:30190425, PubMed:20709748, PubMed:12551911). Interacts with RAP1A (PubMed:20709748). Interacts with KRAS (PubMed:20709748, PubMed:24415755). Interacts with RAC1 (PubMed:20709748, PubMed:12551911). Interacts with RAP1B (PubMed:24415755). Preferentially interacts with prenylated GTPases (PubMed:24415755). Nuclear import is dependent on complexing with a GTPase containing a C-terminal polybasic region. Forms covalent cross-links mediated by transglutaminase TGM2, between a glutamine and the epsilon-amino group of a lysine residue, forming homopolymers and heteropolymers. A chromosomal aberration involving RAP1GDS1 has been found in M0 type acute myeloid leukemia. Translocation (t4;11)(q23;p15) with NUP98. A chromosomal aberration involving RAP1GDS1 has been found in T-cell acute lymphocytic leukemia. Translocation t(4;11)(q23;p15) with NUP98.