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AP3B1A gene on chromosome 5q14.1 that encodes a subunit of the heterotetrameric AP3 complex, a protein complex composed of two large subunits (delta and beta), a medium subunit (mu), and a small subunit (sigma). AP3 plays a role in protein sorting in the late-Golgi/trans-Golgi network (TGN) and/or endosomes, as well as in biogenesis of melanosomes, platelet dense granules and lysosomes. AP3 interacts with clathrin, facilitating the budding of vesicles from the Golgi membrane.
AP3B1 mutations are associated with the Hermansky-Pudlak syndrome, which is characterised by defective lysosome-related organelles.