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J. Bacteriol., Jan 1998, 46-51, Vol 180, No. 1
G Guo and B Weiss
Endonuclease V (deoxyinosine 3' endonuclease), the product of the nfi gene,
has a specificity that encompasses DNAs containing dIMP, abasic sites, base
mismatches, uracil, and even untreated single-stranded DNA. To determine
its importance in DNA repair pathways, nfi insertion mutants and
overproducers (strains bearing nfi plasmids) were constructed. The mutants
displayed a twofold increase in spontaneous mutations for several markers
and an increased sensitivity to killing by bleomycin and nitrofurantoin. An
nfi mutation increased both cellular resistance to and mutability by
nitrous acid. This agent should generate potential cleavage sites for the
enzyme by deaminating dAMP and dCMP in DNA to dIMP and dUMP, respectively.
Relative to that of a wild-type strain, an nfi mutant displayed a 12- to
1,000-fold increase in the frequency of nitrite-induced mutations to
streptomycin resistance, which are known to occur in A x T base pairs. An
nfi mutation also enhanced the lethality caused by a combined deficiency of
exonuclease III and dUTPase, which has been attributed to unrepaired abasic
sites. However, neither the deficiency nor the overproduction of
endonuclease V affected the growth of the single-stranded DNA phages M13 or
phiX174 nor of Uracil-containing bacteriophage lambda. These results
suggest that endonuclease V has a significant role in the repair of
deaminated deoxyadenosine (deoxyinosine) and abasic sites in DNA, but there
was no evidence for its cleavage in vivo of single- stranded or
uracil-containing DNA.
Copyright © 1998, American Society for Microbiology
Endonuclease V (nfi) mutant of Escherichia coli K-12 [In Process Citation]
Department of Pathology, University of Michigan Medical School, Ann Arbor 48109-0602, USA.
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