Analysis of the mechanism by which glucose inhibits maltose induction of MAL gene expression in Saccharomyces.
Expression of the MAL genes required for maltose fermentation in Saccharomyces cerevisiae is induced by maltose and repressed by glucose. Maltose-inducible regulation requires maltose permease and the MAL-activator protein, a DNA-binding transcription factor encoded by MAL63 and its homologues at the other MAL loci. Previously, we showed that the Mig1 repressor mediates glucose repression of MAL gene expression. Glucose also blocks MAL-activator-mediated maltose induction through a Mig1p-independent mechanism that we refer to as glucose inhibition. Here we report the characterization of this process. Our results indicate that glucose inhibition is also Mig2p independent. Moreover, we show that neither overexpression of the MAL-activator nor elimination of inducer exclusion is sufficient to relieve glucose inhibition, suggesting that glucose acts to inhibit induction by affecting maltose sensing and/or signaling. The glucose inhibition pathway requires HXK2, REG1, and GSF1 and appears to overlap upstream with the glucose repression pathway. The likely target of glucose inhibition is Snf1 protein kinase. Evidence is presented indicating that, in addition to its role in the inactivation of Mig1p, Snf1p is required post-transcriptionally for the synthesis of maltose permease whose function is essential for maltose induction.
Hu
Z
Z
Department of Biochemistry, Queens College and Graduate School of CUNY, Flushing, New York 11367, USA.
Yue
Y
Y
Jiang
H
H
Zhang
B
B
Sherwood
P W
PW
Michels
C A
CA
D001483:Base Sequence; D017931:DNA Primers; D005656:Fungal Proteins / Q000235:genetics*; D015966:Gene Expression Regulation, Fungal; D005947:Glucose / Q000378:metabolism*; D008320:Maltose / Q000037:antagonists & inhibitors*; D049990:Membrane Transport Modulators; D026901:Membrane Transport Proteins / Q000037:antagonists & inhibitors / Q000096:biosynthesis; D009004:Monosaccharide Transport Proteins; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000235:genetics* / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors
D017931:DNA Primers; D005656:Fungal Proteins; C120379:MAL63 protein, S cerevisiae; D049990:Membrane Transport Modulators; D026901:Membrane Transport Proteins; D009004:Monosaccharide Transport Proteins; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors; D008320:Maltose; C021534:maltose permease; C071570:SNF1-related protein kinases; D017346:Protein Serine-Threonine Kinases; D005947:Glucose