title: Single-molecule analysis reveals clustering and epigenetic regulation of replication origins at the yeast rDNA locus.
abstract: How eukaryotes specify their replication origins is an important unanswered question. Here, we analyze the replicative organization of yeast rDNA, which consists of approximately 150 identical repeats, each containing a potential origin. Using DNA combing and single-molecule imaging, we show that functional rDNA origins are clustered and interspersed with large domains where initiation is silenced. This repression is largely mediated by the Sir2p histone-deacetylase. Increased origin firing in sir2 Delta mutants leads to the accumulation of circular rDNA species, a major determinant of yeast aging. We conclude that rDNA replication is regulated epigenetically and that Sir2p may promote genome stability and longevity by suppressing replication-dependent rDNA recombination.
mesh_terms: D004261:DNA Replication; D004271:DNA, Fungal / Q000096:biosynthesis*; D004275:DNA, Ribosomal / Q000096:biosynthesis*; D006655:Histone Deacetylases / Q000235:genetics / Q000502:physiology*; D012091:Repetitive Sequences, Nucleic Acid; D018741:Replication Origin; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000502:physiology; D038281:Silent Information Regulator Proteins, Saccharomyces cerevisiae / Q000235:genetics / Q000502:physiology*; D056565:Sirtuin 2; D037761:Sirtuins / Q000235:genetics / Q000502:physiology*
chemical_list: D004271:DNA, Fungal; D004275:DNA, Ribosomal; D038281:Silent Information Regulator Proteins, Saccharomyces cerevisiae; C087778:SIR2 protein, S cerevisiae; D056565:Sirtuin 2; D037761:Sirtuins; D006655:Histone Deacetylases