Molecular analysis of GPH1, the gene encoding glycogen phosphorylase in Saccharomyces cerevisiae.

Abstract

In yeast cells, the activity of glycogen phosphorylase is regulated by cyclic AMP-mediated phosphorylation of the enzyme. We have previously cloned the gene for glycogen phosphorylase (GPH1) in Saccharomyces cerevisiae. To assess the role of glycogen and phosphorylase-catalyzed glycogenolysis in the yeast life cycle, yeast strains lacking a functional GPHI gene or containing multiple copies of the gene were constructed. GPHI was found not to be an essential gene in yeast cells. Haploid cells disrupted in GPHI lacked phosphorylase activity and attained higher levels of intracellular glycogen but otherwise were similar to wild-type cells. Diploid cells homozygous for the disruption were able to sporulate and give rise to viable ascospores. Absence of functional GPHI did not impair cells from synthesizing and storing trehalose. Increases in phosphorylase activity of 10-to 40-fold were detected in cells carrying multiple copies of GPHI-containing 2,um plasmid. Northern (RNA) analysis indicated that GPHI transcription was induced at the late exponential growth phase, almost simultaneous with the onset of intracellular glycogen accumulation. Thus, the low level of glycogen in exponential cells was not primarily maintained through regulating the phosphorylation state of a constitutive amount of phosphorylase. GPHI did not appear to be under formal glucose repression, since transcriptional induction occurred well in advance of glucose depletion from the medium.

Autophagy-assisted glycogen catabolism regulates asexual differentiation inMagnaporthe oryzae

“…G6P is an efficient inhibitor of the active form of Gph1. 41 The addition of 0.5 mM G6P to the growth media caused a remarkable suppression of conidiation defects in the atg8Δ strain (53.2 ± 4.4 x10 2 conidia/cm 2 , from the wild type in terms of its capacity to breach the host surface and cause disease ( Fig. 6A and B).…”

“…Among these was a glycogen phosphorylase of 98 kDa, encoded by MGG_01819, an ortholog of yeast GPH1. 41 In S. cerevisiae, GPH1 is transcriptionally induced at late exponential growth phase, concomitant with the onset of intracellular Glycogen autophagy and Magnaporthe development www.landesbioscience.com Autophagy 37…”

“…The gph1Δ mutant did not differ significantly glycogen accumulation. 41,42 Gph1 acts in the cytoplasm to release G1P from glycogen.…”

Genomic Expression Programs in the Response of Yeast Cells to Environmental Changes

“…The simultaneous induction of both synthetic and catabolic enzymes seems paradoxical. However the activity of many of these enzymes is sensitively controlled at the posttranslational level (Hwang et al, 1989;Marchase et al, 1993;Dey et al, 1994;Huang et al, 1998;Parrou et al, 1999). We propose that the coinduction of these genes renders the cell poised to rapidly and sensitively modulate the activity of the corresponding enzymes and thereby increases the cell's capacity for regulated flux of carbohydrates into and out of its glycogen and trehalose stores.…”

Double Knockout Mutants of Arabidopsis Grown under Normal Conditions Reveal that the Plastidial Phosphorylase Isozyme Participates in Transitory Starch Metabolism

“…Ample evidence has been presented that these enzymes are essential biosynthetic enzymes (Ballicora et al, 2003;Zeeman et al, 2010;Roach et al, 2012;Palm et al, 2013). Furthermore, it is widely accepted that in glycogenstoring cells, phosphorylase is indispensible for the degradation of the storage polysaccharide (Hwang et al, 1989;Alonso-Casajús et al, 2006;Wilson et al, 2010;Roach et al, 2012;Gazzerro et al, 2013).…”