Endonuclease V Protects Escherichia Coli Against Specific Mutations Caused by Nitrous Acid

Mutat Res. 1999 Dec 7;435(3):245-54. doi: 10.1016/s0921-8777(99)00049-x.


Endonuclease V (deoxyinosine 3'-endonuclease) of Escherichia coli K-12 is a putative DNA repair enzyme that cleaves DNA's containing hypoxanthine, uracil, or mismatched bases. An endonuclease V (nfi) mutation was tested for specific mutator effects on a battery of trp and lac mutant alleles. No marked differences were seen in frequencies of spontaneous reversion. However, when nfi mutants were treated with nitrous acid at a level that was not noticeably mutagenic for nfi(+) strains, they displayed a high frequency of A:T-->G:C, and G:C-->A:T transition mutations. Nitrous acid can deaminate guanine in DNA to xanthine, cytosine to uracil, and adenine to hypoxanthine. The nitrous acid-induced A:T-->G:C transitions were consistent with a role for endonuclease V in the repair of deaminated adenine residues. A confirmatory finding was that the mutagenesis was depressed at a locus containing N(6)-methyladenine, which is known to be relatively resistant to nitrosative deamination. An alkA mutation did not significantly enhance the frequency of A:T-->G:C mutations in an nfi mutant, even though AlkA (3-methyladenine-DNA glycosylase II) has hypoxanthine-DNA glycosylase activity. The nfi mutants also displayed high frequencies of nitrous acid-induced G:C-->A:T transitions. These mutations could not be explained by cytosine deamination because an ung (uracil-DNA N-glycosylase) mutant was not similarly affected. However, these findings are consistent with a role for endonuclease V in the removal of deaminated guanine, i.e., xanthine, from DNA. The results suggest that endonuclease V helps to protect the cell against the mutagenic effects of nitrosative deamination.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • DNA Glycosylases*
  • DNA Repair / drug effects
  • DNA Repair / physiology
  • Deoxyribonuclease (Pyrimidine Dimer)
  • Endodeoxyribonucleases / physiology*
  • Escherichia coli / drug effects*
  • Escherichia coli / enzymology
  • Escherichia coli / genetics*
  • Gene Frequency
  • Mutagenesis*
  • Mutagens / pharmacology*
  • N-Glycosyl Hydrolases / genetics
  • Nitrous Acid / pharmacology*
  • Tryptophan / genetics
  • Uracil-DNA Glycosidase


  • Mutagens
  • Tryptophan
  • Endodeoxyribonucleases
  • Deoxyribonuclease (Pyrimidine Dimer)
  • DNA Glycosylases
  • N-Glycosyl Hydrolases
  • Uracil-DNA Glycosidase
  • DNA-3-methyladenine glycosidase II
  • Nitrous Acid