Telomeric and rDNA silencing in Saccharomyces cerevisiae are dependent on a nuclear NAD+ salvage pathway

Joseph J. Sandmeier, Ivana Celic, Jef D. Boeke, Jeffrey S. Smith

Research output: Contribution to journalArticlepeer-review


The Sir2 protein is an NAD+-dependent protein deacetylase that is required for silencing at the silent mating-type loci, telomeres, and the ribosomal DNA (rDNA). Mutations in the NAD+ salvage gene NPT1 weaken all three forms of silencing and also cause a reduction in the intracellular NAD+ level. We now show that mutation of a highly conserved histidine residue in Npt1p results in a silencing defect, indicating that Npt1p enzymatic activity is required for silencing. Deletion of another NAD+ salvage pathway gene called PNC1 caused a less severe silencing defect and did not significantly reduce the intracellular NAD+ concentration. However, silencing in the absence of PNC1 was completely dependent on the import of nicotinic acid from the growth medium. Deletion of a gene in the de novo NAD+ synthesis pathway BNA1 resulted in a significant rDNA silencing defect only on medium deficient in nicotinic acid, an NAD+ precursor. By immunofluorescence microscopy, Myc-tagged Bna1p was localized throughout the whole cell in an asynchronously growing population. In contrast, Myc-tagged Npt1p was highly concentrated in the nucleus in ̃40% of the cells, indicating that NAD+ salvage occurs in the nucleus in a significant fraction of cells. We propose a model in which two components of the NAD+ salvage pathway, Pnc1p and Npt1p, function together in recycling the nuclear nicotinamide generated by Sir2p deacetylase activity back into NAD+.

Original languageEnglish (US)
Pages (from-to)877-889
Number of pages13
Issue number3
StatePublished - 2002

ASJC Scopus subject areas

  • General Medicine


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