title: Suppressors of defective silencing in yeast: effects on transcriptional repression at the HMR locus, cell growth and telomere structure.
abstract: To identify factors that affect transcriptional silencing at the HMR mating-type locus in yeast, we characterized a set of extragenic suppressor mutations that restore metastable repression in cells containing both a mutant silencer-binding protein (rap1s) and a mutated silencer element (hmr delta A). A total of 57 suppressors comprising 21 different complementation groups was identified. This report describes a detailed genetic analysis of these suppressors of defective silencing (sds) mutants. The sds mutants fall into several distinct categories based on secondary phenotypes, such as their ability to suppress the rap1s telomere lengthening phenotype, general effects on telomere length, temperature-dependent growth defects, and the ability to bypass the requirement for cis regulatory elements at the HMR-E silencer. One particular mutant, sds4-1, strongly suppresses the rap1s silencing defect, restores telomeres to nearly wild-type length, and displays a severe growth defect at all temperatures. SDS4 mutations also suppress the silencing defect caused by mutations in the RAP1-interacting factor RIF1. We cloned the SDS4 gene and show that it is identical to GAL11(SPT13), which encodes a component of a protein complex that mediates transcriptional activation. Possible mechanism(s) of suppression by sds4 and the other sds mutations is discussed.
authors.affiliation: Department of Microbiology, College of Physicians & Surgeons of Columbia University, New York, New York 10032, USA.
authors.forename: L
authors.initials: L
authors.lastname: Sussel
authors.forename: D
authors.initials: D
authors.lastname: Vannier
authors.forename: D
authors.initials: D
authors.lastname: Shore
mesh_terms: D015825:Chromosomes, Fungal / Q000648:ultrastructure*; D004268:DNA-Binding Proteins / Q000235:genetics; D005656:Fungal Proteins / Q000235:genetics* / Q000502:physiology; D019204:GTP-Binding Proteins / Q000235:genetics; D015966:Gene Expression Regulation, Fungal / Q000235:genetics; D005800:Genes, Fungal; D016153:Genes, Suppressor; D005816:Genetic Complementation Test; D056892:Mediator Complex; D012097:Repressor Proteins / Q000235:genetics; D012441:Saccharomyces cerevisiae / Q000235:genetics* / Q000254:growth & development; D029701:Saccharomyces cerevisiae Proteins; D016615:Telomere / Q000648:ultrastructure*; D034501:Telomere-Binding Proteins; D015534:Trans-Activators / Q000235:genetics* / Q000502:physiology; D014158:Transcription, Genetic; D020668:rap GTP-Binding Proteins
chemical_list: D004268:DNA-Binding Proteins; D005656:Fungal Proteins; C058337:GAL11 protein, S cerevisiae; D056892:Mediator Complex; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins; D034501:Telomere-Binding Proteins; D015534:Trans-Activators; C074461:RIF1 protein, S cerevisiae; D019204:GTP-Binding Proteins; D020668:rap GTP-Binding Proteins