Proposed to be involved in endosomal maturation implicating in part vps-33.2. May play a role in epithelial polarization through stabilization of apical membrane protein content. May play a role in transcriptional regulation (By similarity). Plays a role in lysosomal trafficking, probably via association with the core HOPS complex in a discrete population of endosomes. Essential for vesicular trafficking during spermatogenesis; required during spermiogenesis or sperm activation for the morphogenesis of specialized Golgi-derived fibrous body-membranous organelle (FB-MO) complexes. Required for the processing of internalized proteins in oocytes and coelomocytes. Interacts with vps-33.1 and vps-33.2 (PubMed:19109425). Associates with the homotypic fusion and vacuole protein sorting (HOPS) complex, impaired by vps-33.2 (By similarity). Localizes in both residual bodies and budding spermatids (PubMed:14504223). Expressed in spermatocytes and spermatids (at protein level). Expressed in the embryonic testis. Mutants produce spermatocytes that complete meiosis but do not usually form functional. Show defective vesicular biogenesis during spermatogenesis with morphogenesis failure of the specialized Golgi-derived fibrous body-membranous organelle (FB-MO) complexes. Show disrupted processing of endocytosed proteins in oocytes and coelomocytes. Belongs to the SPE39 family.