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1
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Bacterial DNA repair genes and their eukaryotic homologues: 3. AlkB dioxygenase and Ada methyltransferase in the direct repair of alkylated DNA

100%
Nieminuszczy J., Grzesiuk E.
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2007
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vol. 54
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issue 3
459-468
EN
Environmental and endogenous alkylating agents generate cytotoxic and mutagenic lesions in DNA. Exposure of prokaryotic cells to sublethal doses of DNA alkylating agents induces so called adaptive response (Ada response) involving the expression of a set of genes which allows the cells to tolerate the toxic and mutagenic action of such agents. The Ada response includes the expression of four genes: ada, alkA, alkB, and aidB. The product of ada gene, Ada protein, is an activator of transcription of all four genes. DNA bases damaged by alkylation are removed by distinct strategies. The most toxic lesion 3meA is removed by specific DNA glycosylase initiating base excising repair. The toxic and mutagenic O6meG is repaired directly by methyltransferases. 1meA and 3meC are corrected by AlkB DNA dioxygenase. The mechanisms of action of E. coli AlkB dioxygenase and its human homologs ABH2 and ABH3 are described in more details.
2
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Mutator specificity of Escherichia coli alkB117 allele

81%
Nieminuszczy J., Janion C., Grzesiuk E.
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2006
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vol. 53
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issue 2
425-428
EN
The Escherichia coli AlkB protein encoded by alkB gene was recently found to repair cytotoxic DNA lesions 1-methyladenine (1-meA) and 3-methylcytosine (3-meC) by using a novel iron-catalysed oxidative demethylation mechanism that protects the cell from the toxic effects of methylating agents. Mutation in alkB results in increased sensitivity to MMS and elevated level of MMS-induced mutations. The aim of this study was to analyse the mutational specificity of alkB117 in a system developed by J.H. Miller involving two sets of E. coli lacZ mutants, CC101-106 allowing the identification of base pair substitutions, and CC107-CC111 indicating frameshift mutations. Of the six possible base substitutions, the presence of alkB117 allele led to an increased level of GC→AT transitions and GC→TA and AT→TA transversions. After MMS treatment the level of GC→AT transitions increased the most, 22-fold. Among frameshift mutations, the most numerous were -2CG, -1G, and -1A deletions and +1G insertion. MMS treatment appreciably increased all of the above types of frameshifts, with additional appearance of the +1A insertion.
3
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Effect of SOS-induced Pol II, Pol IV, and Pol V DNA polymerases on UV-induced mutagenesis and MFD repair in Escherichia coli cells.

81%
Wrzesiński M., Nowosielska A., Nieminuszczy J., Grzesiuk E.
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2005
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vol. 52
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issue 1
139-147
EN
Irradiation of organisms with UV light produces genotoxic and mutagenic lesions in DNA. Replication through these lesions (translesion DNA synthesis, TSL) in Escherichia coli requires polymerase V (Pol V) and polymerase III (Pol III) holoenzyme. However, some evidence indicates that in the absence of Pol V, and with Pol III inactivated in its proofreading activity by the mutD5 mutation, efficient TSL takes place. The aim of this work was to estimate the involvement of SOS-inducible DNA polymerases, Pol II, Pol IV and Pol V, in UV mutagenesis and in mutation frequency decline (MFD), a mechanism of repair of UV-induced damage to DNA under conditions of arrested protein synthesis. Using the argE3→Arg+ reversion to prototrophy system in E. coli AB1157, we found that the umuDC-encoded Pol V is the only SOS-inducible polymerase required for UV mutagenesis, since in its absence the level of Arg+ revertants is extremely low and independent of Pol II and/or Pol IV. The low level of UV-induced Arg+ revertants observed in the AB1157mutD5ΔumuDC strain indicates that under conditions of disturbed proofreading activity of Pol III and lack of Pol V, UV-induced lesions are bypassed without inducing mutations. The presented results also indicate that Pol V may provide substrates for MFD repair; moreover, we suggest that only those DNA lesions which result from umuDC-directed UV mutagenesis are subject to MFD repair.
4
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Spontaneous mutagenesis in exponentially growing and stationary-phase, umuDC-proficient and -deficient, Escherichia coli dnaQ49.

81%
Nowosielska A., Nieminuszczy J., Grzesiuk E.
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vol. 51
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issue 3
683-692
EN
Spontaneous mutations arise not only in exponentially growing bacteria but also in non-dividing or slowly dividing stationary-phase cells. In the latter case mutations are called adaptive or stationary-phase mutations. High spontaneous mutability has been observed in temperature sensitive Escherichia coli dnaQ49 strain deficient in 3'→5' proofreading activity assured by the ε subunit of the main replicative polymerase, Pol III. The aim of this study was to evaluate the effects of the dnaQ49 mutation and deletion of the umuDC operon encoding polymerase V (Pol V) on spontaneous mutagenesis in growing and stationary-phase E. coli cells. Using the argE3OC →Arg+ reversion system in the AB1157 strain, we found that the level of growth-dependent and stationary-phase Arg+ revertants was significantly increased in the dnaQ49 mutant at the non-permissive temperature of 37°C. At this temperature, in contrast to cultures grown at 28°C, SOS functions were dramatically increased. Deletion of the umuDC operon in the dnaQ49 strain led to a 10-fold decrease in the level of Arg+ revertants in cultures grown at 37°C and only to a 2-fold decrease in cultures grown at 28°C. Furthermore, in stationary-phase cultures Pol V influenced spontaneous mutagenesis to a much lesser extent than in growing cultures. Our results indicate that the level of Pol III desintegration, dependent on the temperature of incubation, is more critical for spontaneous mutagenesis in stationary-phase dnaQ49 cells than the presence or absence of Pol V.
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