title: Evolution and Functional Trajectory of Sir1 in Gene Silencing.
abstract: We used the budding yeasts Saccharomyces cerevisiae and Torulaspora delbrueckii to examine the evolution of Sir-based silencing, focusing on Sir1, silencers, the molecular topography of silenced chromatin, and the roles of SIR and RNA interference (RNAi) genes in T. delbrueckii. Chromatin immunoprecipitation followed by deep sequencing (ChIP-Seq) analysis of Sir proteins in T. delbrueckii revealed a different topography of chromatin at the HML and HMR loci than was observed in S. cerevisiae. S. cerevisiae Sir1, enriched at the silencers of HMLα and HMR A: , was absent from telomeres and did not repress subtelomeric genes. In contrast to S. cerevisiae SIR1's partially dispensable role in silencing, the T. delbrueckii SIR1 paralog KOS3 was essential for silencing. KOS3 was also found at telomeres with T. delbrueckii Sir2 (Td-Sir2) and Td-Sir4 and repressed subtelomeric genes. Silencer mapping in T. delbrueckii revealed single silencers at HML and HMR, bound by Td-Kos3, Td-Sir2, and Td-Sir4. The KOS3 gene mapped near HMR, and its expression was regulated by Sir-based silencing, providing feedback regulation of a silencing protein by silencing. In contrast to the prominent role of Sir proteins in silencing, T. delbrueckii RNAi genes AGO1 and DCR1 did not function in heterochromatin formation. These results highlighted the shifting role of silencing genes and the diverse chromatin architectures underlying heterochromatin.
authors.affiliation: Department of Molecular and Cell Biology and California Institute of Quantitative Biology, University of California Berkeley, Berkeley, California, USA.
authors.forename: Aisha
authors.initials: A
authors.lastname: Ellahi
authors.affiliation: Department of Molecular and Cell Biology and California Institute of Quantitative Biology, University of California Berkeley, Berkeley, California, USA jrine@berkeley.edu.
authors.forename: Jasper
authors.initials: J
authors.lastname: Rine
mesh_terms: D001665:Binding Sites; D002503:Centromere; D002874:Chromosome Mapping; D015825:Chromosomes, Fungal; D019143:Evolution, Molecular; D005656:Fungal Proteins / Q000235:genetics* / Q000502:physiology; D015966:Gene Expression Regulation, Fungal; D020868:Gene Silencing; D005800:Genes, Fungal; D012441:Saccharomyces cerevisiae / Q000235:genetics*; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism; D000089804:Shelterin Complex; D038281:Silent Information Regulator Proteins, Saccharomyces cerevisiae / Q000235:genetics* / Q000502:physiology; D016615:Telomere; D034501:Telomere-Binding Proteins / Q000378:metabolism; D055319:Torulaspora / Q000235:genetics*; D014157:Transcription Factors / Q000378:metabolism
chemical_list: D005656:Fungal Proteins; C440829:RAP1 protein, S cerevisiae; C084121:SIR1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D000089804:Shelterin Complex; D038281:Silent Information Regulator Proteins, Saccharomyces cerevisiae; D034501:Telomere-Binding Proteins; D014157:Transcription Factors
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