Key regulator in endo-lysosomal trafficking. Governs early-to-late endosomal maturation, microtubule minus-end as well as plus-end directed endosomal migration and positioning, and endosome-lysosome transport through different protein-protein interaction cascades. Plays important roles in microbial pathogen infection and survival, as well as in participating in the life cycle of viruses (By similarity). (Microbial infection) Interacts with Singapore grouper iridoviral proteins VP69 (ORF69) and VP101 (ORF101). Aggregates into the viral factories in cells infected by Singapore grouper iridovirus (SGIV) in the late stages of the infection. Ubiquitously expressed. Expressed in liver, spleen, kidney, brain, intestine, heart, skin, muscle, gill and stomach. (Microbial infection) Down-regulated at 6 hours post infection, and then up-regulated until 48 hours post infection in spleen cells in response to Singapore grouper iridovirus (SGIV) infection. Belongs to the small GTPase superfamily. Rab family.