The function of Ensembl gene identifier ENSG00000133812 (SBF2, SET binding factor 2) is as follows. Guanine nucleotide exchange factor (GEF) which activates RAB21 and possibly RAB28 (PubMed:20937701, PubMed:25648148). Promotes the exchange of GDP to GTP, converting inactive GDP-bound Rab proteins into their active GTP-bound form (PubMed:20937701, PubMed:25648148). In response to starvation-induced autophagy, activates RAB21 which in turn binds to and regulates SNARE protein VAMP8 endolysosomal transport required for SNARE-mediated autophagosome-lysosome fusion (PubMed:25648148). Acts as an adapter for the phosphatase MTMR2 (By similarity). Increases MTMR2 catalytic activity towards phosphatidylinositol 3,5-bisphosphate and to a lesser extent towards phosphatidylinositol 3-phosphate (By similarity). {ECO:0000250|UniProtKB:E9PXF8, ECO:0000269|PubMed:20937701, ECO:0000269|PubMed:25648148}.