Component of the adaptor complexes which link clathrin to receptors in coated vesicles (Probable). Clathrin-associated protein complexes are believed to interact with the cytoplasmic tails of membrane proteins, leading to their selection and concentration (Probable). Required for many aspects of development and behavior, including negative regulation of vulval differentiation (PubMed:8288128). Required for the dendritic localization of potassium channel kvs-4 in the cholinergic motor neuron DA9 (PubMed:26762178). Adaptor protein complex 1 (AP-1) is a heterotetramer composed of two large adaptins (gamma- and beta'-type subunits), a medium adaptin (mu-type subunit AP47) and a small adaptin (sigma-type subunit AP19) (By similarity). Interacts (via N-terminus) with kvs-4 (PubMed:26762178). Component of the coat surrounding the cytoplasmic face of coated vesicles located at the Golgi complex (By similarity). Association with kvs-4, targets kvs-4 to dendrites (PubMed:26762178). Expressed in the cholinergic motor neuron DA9. Belongs to the adaptor complexes medium subunit family.