Glycogen, a branched polymer of glucose, is a storage molecule whose accumulation is under rigorous control in many cells. In Saccharomyces cerevisiae, glycogen biosynthesis involves three processes: nucleation, elongation, and branching (also known as ramification). The formation of glycogen begins when either Glg1p or Glg2p uses UDP-glucose to self-glucosylate to produce a short alpha (1,4)-glucosyl chain covalently attached to one of their internal tyrosine residues. After the self-glucosylation of Glg1p or Glg2p, glycogen synthase is able to extend the linear alpha (1,4)-glucosyl chains of glycogen by catalyzing the formation of alpha (1,4)-glucosidic bonds from UDP- glucose at the non-reducing ends. Branches can be added into the glycogen molecule by Glc3p, which is the glycogen branching enzyme (EC:220.127.116.11) in S. cerevisiae.
Thon VJ, Vigneron-Lesens C, Marianne-Pepin T, Montreuil J, Decq A, Rachez C, et al. Coordinate regulation of glycogen metabolism in the yeast Saccharomyces cerevisiae. Induction of glycogen branching enzyme. J Biol Chem. 1992 Jul 25;267(21):15224–8. PubMedEurope PMCScholia
Farkas I, Hardy TA, Goebl MG, Roach PJ. Two glycogen synthase isoforms in Saccharomyces cerevisiae are coded by distinct genes that are differentially controlled. J Biol Chem. 1991 Aug 25;266(24):15602–7. PubMedEurope PMCScholia
Mu J, Cheng C, Roach PJ. Initiation of glycogen synthesis in yeast. Requirement of multiple tyrosine residues for function of the self-glucosylating Glg proteins in vivo. J Biol Chem. 1996 Oct 25;271(43):26554–60. PubMedEurope PMCScholia
François J, Parrou JL. Reserve carbohydrates metabolism in the yeast Saccharomyces cerevisiae. FEMS Microbiol Rev. 2001 Jan;25(1):125–45. PubMedEurope PMCScholia