Self-glucosylates, via an inter-subunit mechanism, to form an oligosaccharide primer that serves as substrate for gsy-1. L-tyrosyl-[glycogenin] + UDP-alpha-D-glucose = alpha-D-glucosyl-L-tyrosyl-[glycogenin] + H(+) + UDP [1,4-alpha-D-glucosyl](n)-L-tyrosyl-[glycogenin] + UDP-alpha-D-glucose = [1,4-alpha-D-glucosyl](n+1)-L-tyrosyl-[glycogenin] + H(+) + UDP Divalent metal ions. Required for self-glucosylation. Manganese is the most effective. Glycan biosynthesis; glycogen biosynthesis. Forms a heterooctamer with one molecule of gyg-1 bound to each protomer of the gys-1 homotetramer. The N-terminus of gys-1 is involved in interprotomer contacts with gyg-1. The interaction with gys-1 is required for glycogen production but is not required for gys-1 intrinsic activity. The length of the linker region between residues 387-394 which separates two alpha-helices regulates the size of the glycogen particles synthesized but plays no role in the interaction with gsy-1. Self-glycosylated by the transfer of glucose residues from UDP-glucose to itself, forming an alpha-1,4-glycan of around 10 residues attached to Tyr-194. Belongs to the glycosyltransferase 8 family. Glycogenin subfamily.