Model of GOP-1/UNC-108–mediated phagosome maturation. Apoptotic cells are phagocytosed and delivered to early phagosomes, which recruit RAB-5. GOP-1 acts as a GEF to release GDP-bound UNC-108 from GDI-1, promotes exchange of GDP for GTP, and delivers UNC-108 to the phagosome. This requires RAB-5 through an unknown mechanism (dotted line). UNC-108 then promotes recruitment of lysosomes to the phagosome, in parallel with RAB-14. RAB-5 also promotes RAB-7 recruitment to phagosomes through SAND-1/CCZ-1, which triggers lysosomal fusion with the late phagosome.