title: Activation of basal transcription by a mutation in SIN4, a yeast global repressor, occurs through a mechanism different from activator-mediated transcriptional enhancement.
abstract: The Saccharomyces cerevisiae protein Sin4 has been suggested to affect the transcription of various genes by locally altering chromatin structure. Previous studies have defined two classes of promoters: those which are activated by loss of SIN4 function (termed sin4-responsive promoters) and those which are not activated by sin4 mutations (termed sin4 non-responsive promoters). We analyzed the mechanism of this differential response of the two classes of promoters to a sin4 mutation. The sin4 non-responsive promoters were activated when upstream elements in the promoter region were eliminated. The upstream elements of sin4 non-responsive promoters were, in turn, found to repress the activity of the sin4-responsive promoters in an orientation-independent manner. The sin4-mediated activation was repressed by the Rme1- but not by the Tup1-Ssn6-mediated repression system. Activation of sin4-responsive promoters by Pho4 and the sin4 mutation was additive, and enhancement of transcription driven by sin4-responsive promoters was found to be due to an increase in the basal rate of transcription. The upstream regions in the sin4 non-responsive promoters contained elements that were able to inhibit activation of basal transcription. Based on these observations, we suggest that activation of basal transcription by a mutation in a gene for a global repressor, SIN4, occurs through a mechanism that differs from that responsible for activator-mediated transcriptional enhancement, and we therefore propose that basal transcription and activator-mediated transcription are repressed by different mechanisms.
authors.affiliation: Department of Biotechnology, Graduate School of Engineering, Osaka University, Suita-shi, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Mizuno
authors.forename: S
authors.initials: S
authors.lastname: Harashima
mesh_terms: D001483:Base Sequence; D017931:DNA Primers / Q000235:genetics; D004271:DNA, Fungal / Q000235:genetics; D004268:DNA-Binding Proteins; D005656:Fungal Proteins / Q000235:genetics*; D005800:Genes, Fungal; D017930:Genes, Reporter; D056892:Mediator Complex; D008957:Models, Genetic; D009154:Mutation; D016366:Open Reading Frames; D010957:Plasmids / Q000235:genetics; D011401:Promoter Regions, Genetic; D012097:Repressor Proteins / Q000235:genetics*; D012441:Saccharomyces cerevisiae / Q000235:genetics*; D029701:Saccharomyces cerevisiae Proteins; D015534:Trans-Activators; D014157:Transcription Factors; D015533:Transcriptional Activation
chemical_list: D017931:DNA Primers; D004271:DNA, Fungal; D004268:DNA-Binding Proteins; D005656:Fungal Proteins; D056892:Mediator Complex; C060292:PHO4 protein, S cerevisiae; D012097:Repressor Proteins; C076878:SIN4 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D015534:Trans-Activators; D014157:Transcription Factors