enzyme regulation:Regulated by guanine nucleotide exchange factors (GEFs) which promote the exchange of bound GDP for free GTP.,function:Required for the fusion of plasma membranes and early endosomes.,similarity:Belongs to the small GTPase superfamily. Rab family.,subcellular location:Enriched in stage I melanosomes.,subunit:Binds EEA1. Interacts with RIN1 and GAPVD1, which regulate its pathway, probably by acting as a GEF. Interacts with ALS2CL, UNC84B, ZFYVE20 and RUFY1. Interacts with SGSM1 and SGSM3.,