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Transactivation of Schizosaccharomyces pombe cdt2+ stimulates a Pcu4–Ddb1–CSN ubiquitin ligase

Cong Liu, Marius Poitelea, Adam Watson, Shu‐hei Yoshida, Chikashi Shimoda, Christian Holmberg, Olaf Nielsen, Antony M Carr

Author Affiliations

  1. Cong Liu1,
  2. Marius Poitelea1,
  3. Adam Watson1,
  4. Shu‐hei Yoshida2,
  5. Chikashi Shimoda2,
  6. Christian Holmberg3,
  7. Olaf Nielsen3 and
  8. Antony M Carr*,1
  1. 1 Genome Damage and Stability Centre, University of Sussex, Brighton, UK
  2. 2 Department of Biology, Graduate School of Science, Osaka City University, Osaka, Japan
  3. 3 Department of Genetics, University of Copenhagen, Copenhagen K, Denmark
  1. *Corresponding author. Genome Damage and Stability Centre, University of Sussex, Falmer, Brighton BN1 9RQ, UK. Tel.: +44 1273 678122; Fax +44 1273 678121; E‐mail: a.m.carr{at}sussex.ac.uk
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Abstract

Cullin‐4 forms a scaffold for multiple ubiquitin ligases. In Schizosaccharomyces pombe, the Cullin‐4 homologue (Pcu4) physically associates with Ddb1 and the COP9 signalosome (CSN). One target of this complex is Spd1. Spd1 regulates ribonucleotide reductase (RNR) activity. Spd1 degradation during S phase, or following DNA damage of G2 cells, results in the nuclear export of the small RNR subunit. We demonstrate that Cdt2, an unstable WD40 protein, is a regulatory subunit of Pcu4–Ddb1–CSN ubiquitin ligase. cdt2 deletion stabilises Spd1 and prevents relocalisation of the small RNR subunit from the nucleus to the cytoplasm. cdt2+ is periodically transcribed by the Cdc10/DSC1 transcription factor during S phase and transiently transcribed following DNA damage of G2 cells, corresponding to Spd1 degradation profiles. Cdt2 co‐precipitates with Spd1, and Cdt2 overexpression results in constitutive Spd1 degradation. We propose that Cdt2 incorporation into the Pcu4–Ddb1–CSN complex prompts Spd1 targeting and subsequent degradation and that Cdt2 is a WD40 repeat adaptor protein for Cullin‐4‐based ubiquitin ligase.

  • Received March 11, 2005.
  • Accepted October 7, 2005.
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