title: Nsi1 plays a significant role in the silencing of ribosomal DNA in Saccharomyces cerevisiae.
abstract: In eukaryotic cells, ribosomal DNA (rDNA) forms the basis of the nucleolus. In Saccharomyces cerevisiae, 100-200 copies of a 9.1-kb rDNA repeat exist as a tandem array on chromosome XII. The stability of this highly repetitive array is maintained through silencing. However, the precise mechanisms that regulate rDNA silencing are poorly understood. Here, we report that S. cerevisiae Ydr026c, which we name NTS1 silencing protein 1 (Nsi1), plays a significant role in rDNA silencing. By studying the subcellular localization of 159 nucleolar proteins, we identified 11 proteins whose localization pattern is similar to that of Net1, a well-established rDNA silencing factor. Among these proteins is Nsi1, which is associated with the NTS1 region of rDNA and is required for rDNA silencing at NTS1. In addition, Nsi1 physically interacts with the known rDNA silencing factors Net1, Sir2 and Fob1. The loss of Nsi1 decreases the association of Sir2 with NTS1 and increases histone acetylation at NTS1. Furthermore, Nsi1 contributes to the longevity of yeast cells. Taken together, our findings suggest that Nsi1 is a new rDNA silencing factor that contributes to rDNA stability and lifespan extension in S. cerevisiae.
authors.affiliation: School of Biological Sciences and Research Center for Functional Cellulomics, Institute of Microbiology, Seoul National University, Seoul 151-747, Republic of Korea.
authors.forename: Cheol Woong
authors.initials: CW
authors.lastname: Ha
authors.forename: Min-Kyung
authors.initials: MK
authors.lastname: Sung
authors.forename: Won-Ki
authors.initials: WK
authors.lastname: Huh
mesh_terms: D018797:Cell Cycle Proteins / Q000378:metabolism; D002466:Cell Nucleolus / Q000737:chemistry; D004261:DNA Replication; D004275:DNA, Ribosomal / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism / Q000502:physiology*; D015966:Gene Expression Regulation, Fungal; D020868:Gene Silencing; D009687:Nuclear Proteins / Q000032:analysis / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics* / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism / Q000502:physiology*; D038281:Silent Information Regulator Proteins, Saccharomyces cerevisiae / Q000378:metabolism; D056565:Sirtuin 2 / Q000378:metabolism
chemical_list: D018797:Cell Cycle Proteins; D004275:DNA, Ribosomal; D004268:DNA-Binding Proteins; C105579:FOB1 protein, S cerevisiae; C119300:Net1 protein, S cerevisiae; C574300:Nsi1 protein, S cerevisiae; D009687:Nuclear Proteins; D029701:Saccharomyces cerevisiae Proteins; D038281:Silent Information Regulator Proteins, Saccharomyces cerevisiae; C087778:SIR2 protein, S cerevisiae; D056565:Sirtuin 2