Guanyl-nucleotide exchange factor that regulates small GTPases (By similarity). Converts GDP-bound inactive form of rab-3 and cab-1 to the GTP-bound active forms. Regulator of presynaptic activity that interacts with rab-3 to regulate synaptic vesicle release (PubMed:9136770, PubMed:10970871). Is also a regulator of the cab-1 synaptic transmission pathway (PubMed:10970871). Probably by converting rab-3 to its GTP-bound active form, plays a role in the recruitment of endophilin unc-57 to synaptic vesicles (PubMed:21029864). Probably by activating rab-3 and thus regulating the trafficking of dense-core vesicles, plays a role in AVG neuron-mediated formation of the right axon tract of the ventral nerve cord (PubMed:27116976). Regulates anterior body muscle contractions (aBOC) and the expulsion steps during the defecation motor program (DMP) (PubMed:18852466). Probably by regulating DMP, required for fatty acid uptake by intestinal cells (PubMed:25849533). Interacts with cab-1. Expressed in nearly all neurons. Worms exhibit pleiotropic behavioral defects that are suggestive of reduced synaptic transmission (PubMed:9136770). RNAi-mediated knockdown in the intestine causes a mild defect in the expulsion step of the defecation cycle (PubMed:18852466). Belongs to the MADD family.