Affiliation:
1. Department of Biological Sciences, The University at Albany, State University of New York, Albany, New York 12222
Abstract
ABSTRACT
Exposure of
Escherichia coli
strains deficient in molybdopterin biosynthesis (
moa
) to the purine base
N
-6-hydroxylaminopurine (HAP) is mutagenic and toxic. We show that
moa
mutants exposed to HAP also exhibit elevated mutagenesis, a hyperrecombination phenotype, and increased SOS induction. The
E. coli rdgB
gene encodes a protein homologous to a deoxyribonucleotide triphosphate pyrophosphatase from
Methanococcus jannaschii
that shows a preference for purine base analogs.
moa rdgB
mutants are extremely sensitive to killing by HAP and exhibit increased mutagenesis, recombination, and SOS induction upon HAP exposure. Disruption of the endonuclease V gene,
nfi
, rescues the HAP sensitivity displayed by
moa
and
moa rdgB
mutants and reduces the level of recombination and SOS induction, but it increases the level of mutagenesis. Our results suggest that endonuclease V incision of DNA containing HAP leads to increased recombination and SOS induction and even cell death. Double-strand break repair mutants display an increase in HAP sensitivity, which can be reversed by an
nfi
mutation. This suggests that cell killing may result from an increase in double-strand breaks generated when replication forks encounter endonuclease V-nicked DNA. We propose a pathway for the removal of HAP from purine pools, from deoxynucleotide triphosphate pools, and from DNA, and we suggest a general model for excluding purine base analogs from DNA. The system for HAP removal consists of a molybdoenzyme, thought to detoxify HAP, a deoxyribonucleotide triphosphate pyrophosphatase that removes noncanonical deoxyribonucleotide triphosphates from replication precursor pools, and an endonuclease that initiates the removal of HAP from DNA.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
Cited by
49 articles.
订阅此论文施引文献
订阅此论文施引文献,注册后可以免费订阅5篇论文的施引文献,订阅后可以查看论文全部施引文献