title: The ubiquitin-conjugating enzyme Rad6 (Ubc2) is required for silencing in Saccharomyces cerevisiae.
abstract: It has been previously shown that genes transcribed by RNA polymerase II (RNAP II) are subject to position effect variegation when located near yeast telomeres. This telomere position effect requires a number of gene products that are also required for silencing at the HML and HMR loci. Here, we show that a null mutation of the DNA repair gene RAD6 reduces silencing of the HM loci and lowers the mating efficiency of MATa strains. Likewise, rad6-delta reduces silencing of the telomere-located RNAP II-transcribed genes URA3 and ADE2. We also show that the RNAP III-transcribed tyrosyl tRNA gene, SUP4-o, is subject to position effect variegation when located near a telomere and that this silencing requires the RAD6 and SIR genes. Neither of the two known Rad6 binding factors, Rad18 and Ubr1, is required for telomeric silencing. Since Ubrl is the recognition component of the N-end rule-dependent protein degradation pathway, this suggests that N-end rule-dependent protein degradation is not involved in telomeric silencing. Telomeric silencing requires the amino terminus of Rad6. Two rad6 point mutations, rad6(C88A) and rad6(C88S), which are defective in ubiquitin-conjugating activity fail to complement the silencing defect, indicating that the ubiquitin-conjugating activity of RAD6 is essential for full telomeric silencing.
authors.affiliation: Department of Biological Sciences, University of Illinois at Chicago, 60607, USA.
authors.forename: H
authors.initials: H
authors.lastname: Huang
authors.forename: A
authors.initials: A
authors.lastname: Kahana
authors.forename: D E
authors.initials: DE
authors.lastname: Gottschling
authors.forename: L
authors.initials: L
authors.lastname: Prakash
authors.forename: S W
authors.initials: SW
authors.lastname: Liebman
mesh_terms: D004268:DNA-Binding Proteins / Q000378:metabolism; D005656:Fungal Proteins / Q000378:metabolism; D017353:Gene Deletion; D015966:Gene Expression Regulation, Fungal; D005800:Genes, Fungal; D016681:Genome, Fungal; D008025:Ligases / Q000378:metabolism*; D008074:Lipoproteins / Q000235:genetics; D000072235:Mating Factor; D010455:Peptides / Q000235:genetics; D010675:Pheromones; D012319:RNA Polymerase II; D012320:RNA Polymerase III; D012441:Saccharomyces cerevisiae / Q000235:genetics*; D029701:Saccharomyces cerevisiae Proteins; D016615:Telomere / Q000235:genetics*; D014158:Transcription, Genetic; D044763:Ubiquitin-Conjugating Enzymes; D044767:Ubiquitin-Protein Ligases; D014452:Ubiquitins / Q000378:metabolism
chemical_list: D004268:DNA-Binding Proteins; D005656:Fungal Proteins; D008074:Lipoproteins; C095063:MFA2 protein, S cerevisiae; D010455:Peptides; D010675:Pheromones; C063607:RAD18 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D014452:Ubiquitins; D000072235:Mating Factor; C471606:RAD6 protein, S cerevisiae; D044763:Ubiquitin-Conjugating Enzymes; C066066:UBR1 protein, S cerevisiae; D044767:Ubiquitin-Protein Ligases; D012319:RNA Polymerase II; D012320:RNA Polymerase III; D008025:Ligases