Activator of the kinase cdk-5 (By similarity). In several motor neurons, promotes the polarized trafficking of synaptic vesicles and dense-core vesicles. In the ventral nerve cord, regulates the synaptic localization of the glutamate receptor, glr-1 (PubMed:17671168). In DA motor neurons, regulates axonal transport of synaptic vesicle precursors by inhibiting dynein-mediated retrograde transport (PubMed:20510931). Regulates the polarized distribution of dense-core vesicles in DB motor neurons (PubMed:22699897). May regulate these processes in association with cdk-5 (PubMed:17671168, PubMed:20510931). May also play a role in GABAergic synaptic vesicle localization in the ventral nerve cord (PubMed:16996038). Heterodimer composed of a catalytic subunit cdk-5 and a regulatory subunit cdka-1. Interaction with cdka-1 is required for cdk-5 activation. Presynaptic localization in the axon and punctate localization in the dendrite. Expressed in all classes of neurons in the ventral cord. Accumulation of presynaptic components in the dendrite of DA motor neurons (PubMed:20510931). RNAi-mediated knockdown results in an abnormal distribution of GABAergic synaptic vesicles at synaptic termini of the ventral nerve cord (PubMed:16996038). RNAi-mediated knockdown in combination with exposure to pentylenetetrazole, a GABA antagonist that induces seizures, results in an increased convulsion incidence as compared to wild-type animals (PubMed:16996038). Belongs to the cyclin-dependent kinase 5 activator family.