Interacts with numerous Rab family members, functioning as Rab effector for some, and as GTPase activator for others (PubMed:22654674). GTPase activator for rab-2 (PubMed:22654674). In association with ric-19 activates rab-2 during dense core vesicle maturation in cholinergic motoneurons (PubMed:22654674). Interacts with rab-19 (PubMed:22654674). Interacts with ric-19; the interaction is direct and may be required for the activation of rab-2 and dense vesicle maturation in cholinergic motoneurons (PubMed:22654674). Interacts (via RUN domain) with rund-1 (PubMed:24698274). Does not interact with unc-108 (GTP-bound form) (PubMed:22654674). Co-localizes with ric-19 at cytoplasmic vesicle membranes in neurons. Expressed in neurons in the head, tail and ventral nerve cord (at protein level). RNAi-mediated knockdown results in neuronal dense core vesicle trafficking defects whereby fewer dense core vesicles are transported to axons of the dorsal nerve cord. Belongs to the RUTBC family.