The function of Ensembl gene identifier ENSG00000137955 (RABGGTB, Rab geranylgeranyltransferase subunit beta) is as follows. Catalyzes the transfer of a geranylgeranyl moiety from geranylgeranyl diphosphate to both cysteines of Rab proteins with the C-terminal sequence -XXCC, -XCXC and -CCXX, such as RAB1A, RAB3A, RAB5A and RAB7A (PubMed:7991565). Catalytic subunit of the geranylgeranyl transferase type 3 (GGTase-3) complex (PubMed:31209342, PubMed:32128853). The GGTase-3 complex geranylgeranylates and targets FBXL2 to the cellular membranes, where FBXL2 forms part of the E3 ubiquitin-protein ligase complex SCF(FBXL2) that mediates the degradation of membrane-anchored proteins (PubMed:31209342, PubMed:32128853). The GGTase-3 complex geranylgeranylates Golgi v-SNARE protein YKT6 at 'Cys-194' and this prenylation is required for Golgi SNARE complex assembly (PubMed:32128853). {ECO:0000269|PubMed:31209342, ECO:0000269|PubMed:32128853, ECO:0000269|PubMed:7991565}.