A Fob1 independent role for the Smc5/6 complex in the rDNA that modulates lifespan.

The ribosomal DNA (rDNA) in Saccharomyces cerevisiae is in one tandem repeat array on Chromosome XII. Two spacer regions within each repetitive element, called non-transcribed spacer 1 (NTS1) and NTS2, are important in nucleolar organization. Smc5/6 localizes to both NTS1 and NTS2 and is involved in the regulation of Sir2 and Cohibin binding at NTS1, whereas Fob1 and Sir2 are required for optimal binding of the complex to NTS1 and NTS2, respectively. We demonstrate that Smc5/6 functions in chromatin silencing at NTS1 independently of its role in homologous recombination (HR) when forks pause at the replication fork barrier (RFB). In contrast, when the complex does not localize to the rDNA in nse3-1 mutants, the shortened lifespan correlates with NTS2 homeostasis independently of FOB1 status. Our data identify the importance of Smc5/6 integrity in NTS2 transcriptional silencing and repeat tethering, which in turn underscores rDNA stability and replicative lifespan. HighlightsO_LISmc5/6 is important for transcriptional silencing in the rDNA. C_LIO_LISmc5/6 tethers the rDNA array to the periphery. C_LIO_LITranscriptional silencing of ncRNA at NTS1 and NTS2 is differentially regulated. C_LIO_LISmc5/6 has a role in rDNA maintenance independent of HR processing at the RFB. C_LIO_LIFob1-independent disruption of Smc5/6 at NTS2 leads to lifespan reduction. C_LI