Processive glycosyltransferase involved in the biosynthesis of both the non-bilayer-prone beta-monoglycosyldiacylglycerol and the bilayer-forming membrane lipid glucosyl-galactosyldiacylglycerol and digalactosyl-diacylglycerol. These components contribute to regulate the properties and stability of the membrane. Catalyzes sequentially the transfers of glucosyl or galactosyl residues from UDP-Glc or UDP-Gal to diacylglycerol (DAG) acceptor to form the corresponding beta-glycosyl-DAG (3-O-(beta-D-glycopyranosyl)-1,2-diacyl-sn-glycerol). Then, only beta-galactosyl-DAG (3-O-(beta-D-galactopyranosyl)-1,2-diacyl-sn-glycerol) can act as acceptor to give the beta-glycosyl-beta-galactosyl-DAG product (3-O-(beta-D-glycopyranosyl-(1->6)-D-galactopyranosyl)-1,2-diacyl-sn-glycerol). It can also use alpha-Gal-beta-Gal-DAG, ceramide (Cer) and beta-Gal-Cer as sugar acceptors. The enzyme is supposed to be mainly a galactosyltransferase, with higher glycosyltransferase activity for the addition of the second glycosyl on beta-Gal-DAG as acceptor. The main glycolipid produced in vivo is beta-Glc-beta-Gal-DAG with a beta-1,6 linkage. a 1,2-diacyl-sn-glycerol + UDP-alpha-D-glucose = a 1,2-diacyl-3-O-(beta-D-glucopyranosyl)-sn-glycerol + H(+) + UDP a 1,2-diacyl-sn-glycerol + UDP-alpha-D-galactose = a 1,2-diacyl-3-O-(beta-D-galactosyl)-sn-glycerol + H(+) + UDP a 1,2-diacyl-3-O-(beta-D-galactosyl)-sn-glycerol + UDP-alpha-D-glucose = a 1,2-diacyl-3-O-[beta-D-glucopyranosyl-(1->6)-beta-D-galactopyranosyl]-sn-glycerol + H(+) + UDP a 1,2-diacyl-3-O-(beta-D-galactosyl)-sn-glycerol + UDP-alpha-D-galactose = a 1,2-diacyl-3-O-[beta-D-galactosyl-(1->6)-beta-D-galactosyl]-sn-glycerol + H(+) + UDP Activated by the negatively charged lipid phosphatidylglycerol (PG). The local lipid environment around the enzyme affects both the extent of head group elongation and total amounts of glycolipids produced. Glycolipids such as beta-Gal-DAG, alpha-Gal-beta-Gal-DAG, beta-Glc-beta-Gal-DAG and beta-Gal-Cer are highly immunogenic and are reactive towards IgM antibodies. Glycolipids with a terminal beta-Gal are more reactive than the ones with a beta-Glc residue (PubMed:17697098). Belongs to the glycosyltransferase 2 family.