DNA polymerase X from Deinococcus radiodurans possesses a structure-modulated 3'-->5' exonuclease activity involved in radioresistance

Mol Microbiol. 2006 Apr;60(1):165-76. doi: 10.1111/j.1365-2958.2006.05077.x.


Recently a family X DNA polymerase (PolXDr) was identified in the radioresistant bacterium Deinococcus radiodurans. Knockout cells show a delay in double-strand break repair (DSBR) and an increased sensitivity to gamma-irradiation. Here we show that PolXDr possesses 3'-->5' exonuclease activity that stops cutting close to a loop. PolXDr consists of a DNA polymerase X domain (PolXc) and a Polymerase and Histidinol Phosphatase (PHP) domain. Deletion of the PHP domain abolishes only the structure-modulated but not the canonical 3'-->5' exonuclease activity. Thus, the exonuclease resides in the PolXc domain, but the structure-specificity requires additionally the PHP domain. Mutation of two conserved glycines in the PolXc domain leads to a specific loss of the structure-modulated exonuclease activity but not the exonuclease activity in general. The PHP domain itself does not show any activity. PolXDr is the first family X DNA polymerase that harbours an exonuclease activity. The wild-type protein, the glycine mutant and the two domains were expressed separately in DeltapolXDr cells. The wild-type protein could restore the radiation resistance, whereas intriguingly the mutant proteins showed a significant negative effect on survival of gamma-irradiated cells. Taken together our in vivo results suggest that both PolXDr domains play important roles in DSBR in D. radiodurans.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • DNA / metabolism
  • DNA / radiation effects
  • DNA Damage
  • DNA Repair
  • DNA, Bacterial / metabolism
  • DNA, Bacterial / radiation effects
  • DNA-Directed DNA Polymerase* / chemistry
  • DNA-Directed DNA Polymerase* / genetics
  • DNA-Directed DNA Polymerase* / metabolism
  • Deinococcus / enzymology
  • Deinococcus / genetics
  • Deinococcus / radiation effects*
  • Exonucleases / chemistry
  • Exonucleases / metabolism*
  • Gamma Rays
  • Histidinol-Phosphatase / genetics
  • Histidinol-Phosphatase / metabolism
  • Radiation Tolerance*


  • DNA, Bacterial
  • DNA
  • DNA polymerase X
  • DNA-Directed DNA Polymerase
  • Exonucleases
  • Histidinol-Phosphatase