title: Synergy among differentially regulated repressors of the ribonucleotide diphosphate reductase genes of Saccharomyces cerevisiae.
abstract: The Ssn6/Tup1 general repression complex represses transcription of a number of regulons through recruitment by regulon-specific DNA-binding repressors. Rox1 and Mot3 are Ssn6/Tup1-recruiting, DNA-binding proteins that repress the hypoxic genes, and Rfx1 is a Ssn6/Tup1-recruiting, a DNA-binding protein that represses the DNA damage-inducible genes. We previously reported that Rox1 and Mot3 functioned synergistically to repress a subset of the hypoxic genes and that this synergy resulted from an indirect interaction through Ssn6. We report here cross-regulation between Rox1 and Mot3 and Rfx1 in the regulation of the RNR genes encoding ribonucleotide diphosphate reductase. Using a set of strains containing single and multiple mutations in the repressor encoding genes and lacZ fusions to the RNR2 to -4 genes, we demonstrated that Rox1 repressed all three genes and that Mot3 repressed RNR3 and RNR4. Each repressor could act synergistically with the others, and synergy required closely spaced sites. Using artificial constructs containing two repressor sites, we confirmed that all three proteins could function synergistically but that two Rox1 sites or two Rfx1 sites could not. The significance of this synergy lies in the ability to repress gene transcription strongly under normal growth conditions, and yet allow robust induction under conditions that inactivate only one of the repressors. Since the interaction between the proteins is indirect, the evolution of dually regulated genes requires only the acquisition of closely spaced repressor sites.
authors.affiliation: Department of Biological Sciences, University at Albany/SUNY, 1400 Washington Ave., Albany, New York 12222, USA.
authors.forename: Lee G
authors.initials: LG
authors.lastname: Klinkenberg
authors.forename: Travis
authors.initials: T
authors.lastname: Webb
authors.forename: Richard S
authors.initials: RS
authors.lastname: Zitomer
mesh_terms: D000693:Anaerobiosis / Q000235:genetics; D004249:DNA Damage / Q000235:genetics; D004268:DNA-Binding Proteins / Q000378:metabolism; D005786:Gene Expression Regulation; D015966:Gene Expression Regulation, Fungal; D000071701:Regulatory Factor X Transcription Factors; D012097:Repressor Proteins / Q000378:metabolism*; D012264:Ribonucleotide Reductases / Q000235:genetics*; D012441:Saccharomyces cerevisiae / Q000235:genetics* / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism
chemical_list: D004268:DNA-Binding Proteins; C112006:MOT3 protein, S cerevisiae; C083348:ROX1 protein, S cerevisiae; D000071701:Regulatory Factor X Transcription Factors; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors; D012264:Ribonucleotide Reductases