Involved in the biosynthesis of the antifungal agent validamycin A (PubMed:16632251, PubMed:20981366). Catalyzes the conversion of valienol 1-phosphate to GDP-valienol. Also able to use efficiently ATP as nucleotidyl donor, but other NDP derivatives are less efficient (PubMed:20981366). GTP + H(+) + valienol 1-phosphate = diphosphate + GDP-valienol Can also use Mn(2+) and Co(2+). Cells lacking this gene are unable to produce both validoxylamine A and validamycin A. Belongs to the bacterial/plant glucose-1-phosphate adenylyltransferase family.