The interaction of the Escherichia coli mutD and mutT pathways in the prevention of A:T → C:G transversions

Fowler, Robert G.; Amutan, Maria; Isbell, Roberta J.

doi:10.1016/0027-5107(92)90015-t

Cited by 12 publications

(12 citation statements)

References 44 publications

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“…Our results directly demonstrate the potential for high rates of mutagenesis, specifically A-T-->C G transversions, that can occur through oxidative damage leading to Al G mispairing with a defective mutT gene. It has been shown in vivo that DNA polymerase III proofreading removes some mutT-caused A * G mispairings (9), and in vitro studies (22) have shown that the T4 polymerase proofreading prevents A * 8-oxodGMP mispairings. Thus, at least two mechanisms limit the stable incorporation of 8-oxodGTP at the replication fork, and other correction mechanisms exist to remove 8-oxodG from chromosomal DNA (19).…”

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confidence: 99%

Activity of the Escherichia coli mutT mutator allele in an anaerobic environment

1994

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Mutation frequencies for an Escherichia coli mutT strain were measured in both aerobic and anaerobic environments. When cells were grown in a rich medium (L broth), mutation frequencies were similar in both aerobic and anaerobic conditions. In contrast, when grown in a minimal medium, mutT anaerobic mutation frequencies were reduced dramatically compared with aerobic values, which were similar to L broth frequencies. L broth mutT cultures treated with a commercial enzyme complex that reduces free oxygen in the medium also showed strongly reduced anaerobic mutation frequencies. These results indicate that the biological role of the MutT protein is to prevent oxidative damage from becoming mutagenic.Although the mutT mutator allele was the first to be described in Escherichia coli (25), its mechanism of activity has remained unclear until recently. An early key to the nature of mutT activity was the observation that this mutator causes exclusively A* T--C G transversions (27). These transversions arise through A* G mispairings rather than T-C intermediates (2, 23). The MutT protein catalyzes the hydrolysis of nucleoside triphosphates with a preference for dGTP (5, 6), and it was suggested that the biological role of MutT might be to hydrolyze dGTP before it could mispair with a template adenine during DNA replication (5). Recently, Maki and Sekiguchi (17) showed that 8-oxo-7,8-dihydro-2'-dGTP (8-oxodGTP) is more readily hydrolyzed to the monophosphate than dGTP and hypothesized that the MutT protein might act to remove 8-oxodGTP from the nucleotide pool during DNA replication because of its increased tendency to mispair with template adenine compared with that of dGTP (8,16,17,22).8-OxodGTP may be produced in the cell from dGTP by ionizing radiation and oxygen radical-producing chemicals (13-15) as well as from physiological and biochemical processes occurring during normal cellular metabolism (4). It is widely accepted that active partial reduction products of oxygen, i.e., superoxide, hydrogen peroxide, and hydroxyl radical, produced during aerobic respiration, are capable of directly (hydroxyl radical) or indirectly (superoxide radical and hydrogen peroxide) forming oxidative products with DNA and precursor molecules (3, 10, 11). 8-oxodGTP may be among the most abundant of these oxidative products in both bacteria and animals (21, 24). mutT homologs have been found in other bacteria (7,12,18), and a similar nucleoside triphosphatase activity has been found in human cells (20), suggesting that misincorporation of 8-oxodGTP may be a common problem.If MutT does function to remove 8-oxodGTP from nucleotide pools, it might be expected that mutT strains would show lower mutation frequencies in an anaerobic environment than in an aerobic environment. We tested this prediction by measuring mutT mutation frequencies inside an anaerobic * Corresponding author. Phone: (408) Cells were grown in L broth supplemented with glucose (1% tryptone, 0.5% yeast extract, 0.1% glucose, and 0.5% NaCl) or in minimal medium (0.2% glu...

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confidence: 99%

Activity of the Escherichia coli mutT mutator allele in an anaerobic environment

1994

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“…This was found to be the case at two sites examined in the trpA gene [55]. It was estimated that proofreading reduced the mutT ‐induced mispairings at the trpA58 site by about 10‐fold, and at the trpA88 site by about 3‐fold [55]. Since proofreading contributes significantly more (∼200‐fold [31]) to correction of normal transversion mispairs, it may be concluded that A·(8‐oxoG) mispairs are proofread only moderately, although the precise extent is likely sequence dependent.…”

Section: Interaction Of Mutt With Other Fidelity Systemsmentioning

confidence: 73%

“…If the A·(8‐oxoG) mispairings occurring in mutT strains are susceptible to proofreading, the mutation frequency in the mutTmutD5 double mutator strain should exceed simple additivity of the two single mutators. This was found to be the case at two sites examined in the trpA gene [55]. It was estimated that proofreading reduced the mutT ‐induced mispairings at the trpA58 site by about 10‐fold, and at the trpA88 site by about 3‐fold [55].…”

Section: Interaction Of Mutt With Other Fidelity Systemsmentioning

confidence: 91%

“…The trpA58 reversion frequency in mut + cells is approximately 8×10 −9 with about 10% of the resulting Trp + revertants arising from A·T→C·G transversions at a single nucleotide position [54]. The presence of mutT increases the frequency to approximately (2–3)×10 −6 [54, 55]with almost all (>98%) of the revertants resulting from A·T→C·G transversions [54, 55], representing a 2500–3750‐fold increase in A·T→C·G transversions. However, while practically all A·T→C·G transversions in the mutT strain occur through the mutT pathway, only a proportion of the A·T→C·G transversions do so in mut + cells.…”

Section: Interaction Of Mutt With Other Fidelity Systemsmentioning

confidence: 99%

“…A possible role of proofreading in preventing A·T→C·G transversions was explored using the trpA reversion system [55]. The dnaQ gene produces the ϵ subunit of the DNA polymerase III core, which possesses the 3′→5′ exonuclease activity for proofreading [6].…”

Section: Interaction Of Mutt With Other Fidelity Systemsmentioning

confidence: 99%

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The role of themutTgene ofEscherichia coliin maintaining replication fidelity

Fowler

Schaaper

1997

FEMS Microbiol Rev

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Spontaneous mutation levels are kept low in most organisms by a variety of error-reducing mechanisms, some of which ensure a high level of fidelity during DNA replication. The mutT gene of Escherichia coli is an important participant in avoiding such replication mistakes. An inactive mutT allele is a strong mutator with strict mutational specificity: only A.T-->C.G transversions are enhanced. The biological role of the MutT protein is thought to be the prevention of A.G mispairs during replication, specifically the mispair involving a template A and an oxidized form of guanine, 8-oxoguanine, which results when the oxidized form of dGTP, 8-oxodGTP, is available as a polymerase substrate. MutT is part of an elaborate defense system that protects against the mutagenic effects of oxidized guanine as a part of substrate dGTP and chromosomal DNA. The A.G mispairings prevented by MutT are not well-recognized and/or repaired by other fidelity mechanisms such as proofreading and mismatch repair, accounting in part for the high mutator activity of mutT. MutT is a nucleoside triphosphatase with a preference for the syn form of dGTP, hydrolyzing it to dGMP and pyrophosphate. 8-oxodGTP is hydrolyzed 10 times faster than dGTP, making it a likely biological substrate for MutT. MutT is assumed to hydrolyze 8-oxodGTP in the nucleotide pool before it can be misincorporated. While the broad role of MutT in error avoidance seems resolved, important details that are still unclear are pointed out in this review.

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Base analog N6-hydroxylaminopurine mutagenesis in Escherichia coli: genetic control and molecular specificity

Pavlov

Суслов

Shcherbakova

et al. 1996

Mutation Research/Fundamental and Molecular Mechanisms of Mutag

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The interaction of the Escherichia coli mutD and mutT pathways in the prevention of A:T → C:G transversions

Cited by 12 publications

References 44 publications

Activity of the Escherichia coli mutT mutator allele in an anaerobic environment

Activity of the Escherichia coli mutT mutator allele in an anaerobic environment

The role of themutTgene ofEscherichia coliin maintaining replication fidelity

Base analog N6-hydroxylaminopurine mutagenesis in Escherichia coli: genetic control and molecular specificity

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