Involved in the assembly of the O-repeating unit during O-antigen biosynthesis. an N-acetyl-alpha-D-galactosaminyl derivative + UDP-alpha-D-galactose = a beta-D-galactosyl-(1->3)-N-acetyl-alpha-D-galactosaminyl derivative + H(+) + UDP alpha-D-GalNAc-(1->3)-alpha-D-GalNAc-di-trans,octa-cis-undecaprenyl diphosphate + UDP-alpha-D-galactose = beta-D-Gal-(1->3)-alpha-D-GalNAc-(1->3)-alpha-D-GalNAc-di-trans,octa-cis-undecaprenyl diphosphate + H(+) + UDP Bacterial outer membrane biogenesis; LPS O-antigen biosynthesis. O86:H2 and O86:B7 subtypes share the same O unit, but the O units are polymerized from different terminal sugars in different glycosidic linkages. Belongs to the glycosyltransferase 2 family. Truncated N-terminus.