Fig. 1. Nomenclature and structure of AP-3 subunit isoforms. (A) AP-3 subunit genes and their corresponding gene products. The pattern of expression of each subunit is described as neuronal, corresponding to neurons and neuro-endocrine tissue, or ubiquitous, for subunits expressed in all cells including neuronal tissues. Mice carrying natural or engineered AP-3 subunit deficiencies are listed. (B) Proposed subunit composition of the neuronal and ubiquitous AP-3 isoforms. Both AP-3 complexes can carry either a 3A or a 3B subunit. (C) Adaptor complexes possess three defined domains. The ears correspond to the C-terminal domains of and 3. The trunk or core is composed of a protease-resistant core formed by fragments of 3 and as well as full-length µ3 and 3 subunits. The ears and trunk are connected by hinges.