Flavonol 3-O-glucoside/galactoside (1->2) glucosyltransferase converting kaempferol 3-O-glucoside to kaempferol 3-O-sophoroside. Has a broad in vitro activity for kaempferol/quercetin 3-O-glucoside/galactoside derivatives, but cannot glucosylate kaempferol 3-O-rhamnosyl-(1->4)-[rhamnosyl-(1->6)- glucoside] and 3-O-rhamnosyl-(1->4)-[glucosyl-(1->6)-glucoside]. Has a higher preference for UDP-glucose than UDP-galactose, and no activity with UDP-arabinose and UDP-glucuronic acid. Represents probably a dominant allele of the gene. a flavonol 3-O-beta-D-glucoside + UDP-alpha-D-glucose = a flavonol 3-O-beta-D-glucosyl-(1->2)-beta-D-glucoside + H(+) + UDP Expressed in leaves. Flavonol glycosides (FGs) with glucose at the 2''-position of glucose or galactose at the 3-position of kaempferol are present in cv. Nezumisaya and absent in cv. Harosoy, whereas FGs with glucose at the 6''-position of glucose or galactose at the 3''-position of kaempferol are present in cv. Harosoy and absent in cv. Nezumisaya. Belongs to the UDP-glycosyltransferase family.