Involved in the biosynthesis of the antifungal agent validamycin A (PubMed:16725283). Catalyzes the conversion of valienol 1-phosphate to GDP-valienol and less effectively to ADP-valienol or other NDP derivatives (PubMed:21766819). GTP + H(+) + valienol 1-phosphate = diphosphate + GDP-valienol Belongs to the bacterial/plant glucose-1-phosphate adenylyltransferase family. Was originally thought to be a glucose 1-phosphate uridylyltransferase.