Involved in the biosynthesis of the antifungal agent validamycin A (PubMed:16632251). Catalyzes the final attachment of glucose from UDP-alpha-D-glucose to validoxylamine A to yield validamycin A (PubMed:16632251, PubMed:18563934). UDP-glucose is the most efficient glycosyl donor, whereas GDP-glucose and ADP-glucose are much less efficient (PubMed:16632251). ValG also utilizes UDP-galactose as substrate to produce the new validamycin analog, 4''-epi-validamycin A (PubMed:18563934). UDP-alpha-D-glucose + validoxylamine A = H(+) + UDP + validamycin A Also able to use Mg(2+), Co(2+) and Ca(2+). Instead of having the common DXD motif at the position 99-101, it contains a DTG sequence, which may provide greater metal ion binding flexibility. Cells lacking this gene are unable to produce validamycin A, and show an accumulation of validoxylamine. Belongs to the glycosyltransferase 2 family.