Transfers the glycosyl residue from UDP-Glc to the non-reducing end of alpha-1,4-glucan. Is believed to regulate the synthesis of glycogen. [(1->4)-alpha-D-glucosyl](n) + UDP-alpha-D-glucose = [(1->4)-alpha-D-glucosyl](n+1) + H(+) + UDP Allosteric activation by glucose-6-phosphate, and phosphorylation by a cAMP-dependent kinase. Glycan biosynthesis; glycogen biosynthesis. Interacts with PCL10. Phosphorylated by the cyclin-CDK PCL10-PHO85. Phosphorylation causes inactivation of enzyme. Present with 14600 molecules/cell in log phase SD medium. Belongs to the glycosyltransferase 3 family.