The role of ubiquitin conjugation in glucose-induced proteolysis of Saccharomyces maltose permease.
In Saccharomyces, the addition of glucose induces a rapid degradation of maltose permease that is dependent on endocytosis and vacuolar proteolysis (Medintz, I., Jiang, H., Han, E. K., Cui, W., and Michels, C. A. (1996) J. Bacteriol. 178, 2245-2254). Here we report on the role of ubiquitin conjugation in this process. Deletion of DOA4, which causes decreased levels of available ubiquitin, severely decreases the rate of glucose-induced proteolysis, and this is suppressed by the overproduction of ubiquitin. Overexpression of ubiquitin in an endocytosis-deficient end3-ts strain results in the glucose-stimulated accumulation of a larger molecular weight species of maltose permease, which we demonstrate is a ubiquitin-modified form of the protein by utilizing two ubiquitin alleles with different molecular weights. The size of this ubiquitinated species of maltose permease is consistent with monoubiquitination. A promoter mutation that reduces expression of RSP5/NPI1, a postulated ubiquitin-protein ligase, dramatically reduces the rate of glucose-induced proteolysis of maltose permease. The role of various ubiquitin-conjugating enzymes was investigated using strains carrying mutant alleles ubc1Delta ubc4Delta, ubc4Delta ubc5Delta, cdc34-ts2/ubc3, and ubc9-ts. Loss of these functions was not shown to effect glucose-induced proteolysis of maltose permease, but loss of Ubc1, -4, and -5 was found to inhibit maltose permease expression at the post-transcriptional level.
Medintz
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I
Biology Department, Queens College and the Graduate School of the City University of New York, Flushing, New York 11367, USA.
Jiang
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H
Michels
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CA
D004705:Endocytosis; D056827:Endosomal Sorting Complexes Required for Transport; D005656:Fungal Proteins / Q000235:genetics; D015966:Gene Expression Regulation, Fungal / Q000187:drug effects / Q000502:physiology; D005947:Glucose / Q000494:pharmacology*; D007700:Kinetics; D008025:Ligases / Q000235:genetics* / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D009004:Monosaccharide Transport Proteins; D016296:Mutagenesis; D010957:Plasmids; D011401:Promoter Regions, Genetic; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins; D043743:Ubiquitin-Protein Ligase Complexes; D044767:Ubiquitin-Protein Ligases; D014452:Ubiquitins / Q000378:metabolism*; D014617:Vacuoles / Q000378:metabolism
D056827:Endosomal Sorting Complexes Required for Transport; D005656:Fungal Proteins; D026901:Membrane Transport Proteins; D009004:Monosaccharide Transport Proteins; D029701:Saccharomyces cerevisiae Proteins; D014452:Ubiquitins; C021534:maltose permease; D043743:Ubiquitin-Protein Ligase Complexes; D044767:Ubiquitin-Protein Ligases; D008025:Ligases; C469287:RSP5 protein, S cerevisiae; D005947:Glucose