The Saccharomyces cerevisiae Cdc68 transcription activator is antagonized by San1, a protein implicated in transcriptional silencing.
The CDC68 gene (also called SPT16) encodes a transcription factor for the expression of a diverse set of genes in the budding yeast Saccharomyces cerevisiae. To identify other proteins that are functionally related to the Cdc68 protein, we searched for genetic suppressors of a cdc68 mutation. Four suppressor genes in which mutations reverse the temperature sensitivity imposed by the cdc68-1 mutation were found. We show here that one of the suppressor genes is the previously reported SAN1 gene; san1 mutations were originally identified as suppressors of a sir4 mutation, implicated in the chromatin-mediated transcriptional silencing of the two mating-type loci HML and HMR. Each san1 mutation, including a san1 null allele, reversed all aspects of the cdc68 mutant phenotype. Conversely, increased copy number of the wild-type SAN1 gene lowered the restrictive temperature for the cdc68-1 mutation. Our findings suggest that the San1 protein antagonizes the transcriptional activator function of the Cdc68 protein. The identification of san1 mutations as suppressors of cdc68 mutations suggests a role for Cdc68 in chromatin structure.
Xu
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Department of Microbiology and Immunology, Dalhousie University, Halifax, Nova Scotia, Canada.
Johnston
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GC
Singer
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RA
D000483:Alleles; D018797:Cell Cycle Proteins; D016213:Cyclins / Q000235:genetics; D005656:Fungal Proteins / Q000235:genetics*; D005800:Genes, Fungal; D049770:Genes, Mating Type, Fungal; D016153:Genes, Suppressor; D006657:Histones / Q000235:genetics; D009154:Mutation; D010641:Phenotype; D012441:Saccharomyces cerevisiae / Q000235:genetics*; D029701:Saccharomyces cerevisiae Proteins; D015534:Trans-Activators / Q000235:genetics*; D014157:Transcription Factors; D014158:Transcription, Genetic; D035602:Transcriptional Elongation Factors
D018797:Cell Cycle Proteins; D016213:Cyclins; D005656:Fungal Proteins; D006657:Histones; C071238:SPT16 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D015534:Trans-Activators; D014157:Transcription Factors; D035602:Transcriptional Elongation Factors