GTPase signaling protein that binds to and hydrolyzes GTP. Regulates signaling pathways involving G-proteins-coupled receptor and heterotrimeric proteins such as GNB1, GNB2 and GNB3. May be involved in selected striatal competencies, mainly locomotor activity and motor coordination. Monomer (Potential). Interacts with PIK3CA and UBE2I (By similarity). Interacts with GNB1, GNB2 and GNB3. Interacts with HTT; interacts with mutant HTT (mHTT) with a much higher affinity than wild type HTT. Pancreatic endocrine cells (islets of Langerhans). Farnesylated. Farnesylation is required for membrane targeting (By similarity). Reduces cell survival in striatal cells with Huntington disease by binding to mutant Huntington disease protein (mHTT; poly-Gln region with 82 repeats) and inducing sumoylation of mHTT. Belongs to the small GTPase superfamily. RasD family. Extended N-terminus.