BLOC-1 subunit 3 is a protein that in humans is encoded by the BLOC1S3 gene. This protein is a component of BLOC-1 (Biogenesis of lysosome-related organelles complex), which is involved in the biogenesis of certain organelles like melanosomes and dense granules in platelets. Also called HPS8, mutations in the gene BLOC1S3 are associated with type 8 Hermansky–Pudlak syndrome.