Glycogen synthesis in the absence of glycogenin in the yeast Saccharomyces cerevisiae.
In eukaryotic cells, glycogenin is a self-glucosylating protein that primes glycogen synthesis. In yeast, the loss of function of GLG1 and GLG2, which encode glycogenin, normally leads to the inability of cells to synthesize glycogen. In this report, we show that a small fraction of colonies from glg1glg2 mutants can switch on glycogen synthesis to levels comparable to wild-type strain. The occurrence of glycogen positive glg1glg2 colonies is strongly enhanced by the presence of a hyperactive glycogen synthase and increased even more upon deletion of TPS1. In all cases, this phenotype is reversible, indicating the stochastic nature of this synthesis, which is furthermore illustrated by colour-sectoring of colonies upon iodine-staining. Altogether, these data suggest that glycogen synthesis in the absence of glycogenin relies on a combination of several factors, including an activated glycogen synthase and as yet unknown alternative primers whose synthesis and/or distribution may be controlled by TPS1 or under epigenetic silencing.
Torija
María-Jesús
MJ
Centre Bioingenierie Gilbert Durand, UMR-CNRS 5504, UMR-INRA 792, Institut National des Sciences Appliquées, 31077 Toulouse Cedex 04, France.
Novo
Maite
M
Lemassu
Anne
A
Wilson
Wayne
W
Roach
Peter J
PJ
François
Jean
J
Parrou
Jean-Luc
JL
D003470:Culture Media / Q000494:pharmacology; D044127:Epigenesis, Genetic; D020868:Gene Silencing; D005947:Glucose / Q000378:metabolism; D005964:Glucosyltransferases / Q000378:metabolism; D006003:Glycogen / Q000737:chemistry / Q000378:metabolism*; D006006:Glycogen Synthase / Q000737:chemistry / Q000378:metabolism; D006023:Glycoproteins / Q000737:chemistry / Q000378:metabolism*; D007455:Iodine / Q000737:chemistry / Q000494:pharmacology; D009682:Magnetic Resonance Spectroscopy; D009154:Mutation; D010641:Phenotype; D010957:Plasmids / Q000378:metabolism; D011522:Protons; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry; D013997:Time Factors
D003470:Culture Media; D006023:Glycoproteins; D011522:Protons; D029701:Saccharomyces cerevisiae Proteins; C051887:glycogenin; D006003:Glycogen; D007455:Iodine; D005964:Glucosyltransferases; D006006:Glycogen Synthase; C023180:trehalose-6-phosphate synthase; D005947:Glucose