Ddb1 controls genome stability and meiosis in fission yeast (original) (raw)

  1. Christian Holmberg1,4,
  2. Oliver Fleck1,2,4,
  3. Heidi A. Hansen1,5,
  4. Cong Liu3,
  5. Rita Slaaby1,6,
  6. Antony M. Carr3, and
  7. Olaf Nielsen1,7
  8. 1Department of Genetics, Institute of Molecular Biology, University of Copenhagen, DK-1353 Copenhagen K, Denmark; 2North West Cancer Research Fund Institute, University of Wales, Bangor, Gwynedd LL57 2UW, United Kingdom; 3Genome Damage and Stability Centre, School of Life Sciences, University of Sussex, Falmer, Sussex BN1 9RQ, United Kingdom

Abstract

The human UV-damaged DNA-binding protein Ddb1 associates with cullin 4 ubiquitin ligases implicated in nucleotide excision repair (NER). These complexes also contain the signalosome (CSN), but NER-relevant ubiquitination targets have not yet been identified. We report that fission yeast Ddb1, Cullin 4 (Pcu4), and CSN subunits Csn1 and Csn2 are required for degradation of the ribonucleotide reductase (RNR) inhibitor protein Spd1. Ddb1-deficient cells have >20-fold increased spontaneous mutation rate. This is partly dependent on the error-prone translesion DNA polymerases. Spd1 deletion substantially reduced the mutation rate, suggesting that insufficient RNR activity accounts for ∼50% of observed mutations. Epistasis analysis indicated that Ddb1 contributed to mutation avoidance and tolerance to DNA damage in a pathway distinct from NER. Finally, we show that Ddb1/Csn1/Cullin 4-mediated Spd1 degradation becomes essential when cells differentiate into meiosis. These results suggest that Ddb1, along with Cullin 4 and the signalosome, constitute a major pathway controlling genome stability, repair, and differentiation via RNR regulation.

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