General Rab protein regulator required for vesicle formation from the Golgi complex. May control vesicle docking and fusion by mediating the action of Rab GTPases to the SNARE complexes. In addition it inhibits the removal of Rab GTPases from the membrane by GDI1. Homodimers (By similarity). Interacts specifically with both prenylated Rab proteins (including RAB3A and RAB1), and VAMP2 (synaptobrevin-2), in an exclusive way. Interacts with NDRG1 (By similarity). Interacts with free GDI1 in the absence of Rab proteins. Also interacts with PCLO. According to some authors, it is an integral membrane protein, while others showed that it is cytoplasmic and membrane-associated to Golgi (PubMed:10751420, PubMed:12107180, PubMed:11096102) and synaptic vesicles (PubMed:10707984). Ubiquitous. Belongs to the PRA1 family. In contrast to the mouse ortholog, it does not interact with the Ras-like GTPases RAC1 and RHOA.