A novel DNA damage response: rapid degradation of the p12 subunit of dna polymerase delta

J Biol Chem. 2007 May 25;282(21):15330-40. doi: 10.1074/jbc.M610356200. Epub 2007 Feb 21.


Mammalian DNA polymerase (Pol) delta is essential for DNA replication. It consists of four subunits, p125, p50, p68, and p12. We report the discovery that the p12 subunit is rapidly degraded in cultured human cells by DNA damage or replication stress brought about by treatments with UV, methyl methanesulfonate, hydroxyurea, and aphidicolin. The degradation of p12 is due to an accelerated rate of proteolysis that is inhibited by the proteasome inhibitors, MG132 and lactacystin. UV treatment converts Pol delta in vivo to the three-subunit form lacking p12. This was demonstrated by its isolation using immunoaffinity chromatography. The three-subunit enzyme retains activity on poly(dA)/oligo(dT) templates but is impaired in its ability to extend singly primed M13 templates, clearly indicating that its in vivo functions are likely to be compromised. This transformation of Pol delta by modification of its quaternary structure is reversible in vitro by the addition of the p12 subunit and could represent a novel in vivo mechanism for the modulation of Pol delta function. UV and hydroxyurea-triggered p12 degradation is blocked in ATR(-/-) cells but not in ATM(-/-) cells, thereby demonstrating that p12 degradation is regulated by ATR, the apical kinase that regulates the damage response in S-phase. These findings reveal a novel addition to the cellular repertoire of DNA damage responses that also impacts our understanding of the role of Pol delta in both DNA replication and DNA repair.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Ataxia Telangiectasia Mutated Proteins
  • Cell Cycle Proteins / genetics
  • Cell Cycle Proteins / metabolism*
  • DNA Damage* / drug effects
  • DNA Damage* / radiation effects
  • DNA Polymerase III / chemistry
  • DNA Polymerase III / genetics
  • DNA Polymerase III / metabolism*
  • DNA Replication* / drug effects
  • DNA Replication* / radiation effects
  • DNA-Binding Proteins / genetics
  • DNA-Binding Proteins / metabolism
  • Enzyme Inhibitors / pharmacology
  • HeLa Cells
  • Humans
  • Proteasome Endopeptidase Complex / metabolism
  • Proteasome Inhibitors
  • Protein Processing, Post-Translational* / drug effects
  • Protein Processing, Post-Translational* / radiation effects
  • Protein Serine-Threonine Kinases / genetics
  • Protein Serine-Threonine Kinases / metabolism*
  • Protein Subunits / chemistry
  • Protein Subunits / genetics
  • Protein Subunits / metabolism
  • Tumor Suppressor Proteins / genetics
  • Tumor Suppressor Proteins / metabolism
  • Ultraviolet Rays


  • Cell Cycle Proteins
  • DNA-Binding Proteins
  • Enzyme Inhibitors
  • Proteasome Inhibitors
  • Protein Subunits
  • Tumor Suppressor Proteins
  • ATM protein, human
  • ATR protein, human
  • Ataxia Telangiectasia Mutated Proteins
  • Protein Serine-Threonine Kinases
  • POLD4 protein, human
  • DNA Polymerase III
  • Proteasome Endopeptidase Complex