Interacts with numerous Rab family members, functioning as Rab effector for some, and as GTPase activator for others. Promotes GTP hydrolysis by RAB34 and RAB36. Probably functions as GTPase effector with RAB9A and RAB9B; does not stimulate GTP hydrolysis with RAB9A and RAB9B. Interacts with RAB9A (GTP-bound form) and RAB9B (GTP-bound form); has much lower affinity for GDP-bound RAB9A and RAB9B (PubMed:22637480). Interacts with RAB3A, RAB4A, RAB5A, RAB8A, RAB11A, RAP1A, RAP1B, RAP2A and RAP2B. No interaction with RAB27A (PubMed:17509819). Recruited to cytoplasmic vesicle membranes via its interaction with Rab family members, such as RAB9A. Mainly expressed in brain, heart and testis. Belongs to the RUTBC family.