This family is most closely related to the GT5 family of glycosyltransferases. Glycogen synthase (EC:2.4.1.21) catalyzes the formation and elongation of the alpha-1,4-glucose backbone using ADP-glucose, the second and key step of glycogen biosynthesis. This family includes starch synthases of plants, such as DULL1 in Zea mays and glycogen synthases of various organisms.