Biomedical subjects

J Laval

Publications and source records attributed to J Laval.

At least 19 recordsLinked to original sources

PubMed2001

Characterization of thermal stability of the Escherichia coli Fapy-DNA glycosylase.

Thermal stability of Escherichia coli Fpg protein was studied using far-UV circular dichroism and intrinsic fluorescence. Experimental data indicate that Fpg irreversibly aggregates under heating above 35 degrees C. Heat aggregation is preceded by tertiary conformational changes of Fpg. However, the secondary structure of the fraction that does not aggregate remains unchanged up to approximately 60 degrees C. The kinetics of heat aggregation occurs with an activation enthalpy of approximately 21 kcal/mol. The fraction of monomers forming aggregates decreases with increasing urea concentration, with essentially no aggregation observed above approximately 3 M urea, suggesting that heat aggregation results from hydrophobic association of partially unfolded proteins. With increasing urea concentration, Fpg unfolds in a two-state reversible transition, with a stability of approximately 3.6 kcal/mol at 25 degrees C. An excellent correlation is observed between the unfolded fraction and loss of activity of Fpg. A simple kinetic scheme that describes both the rates and the extent of aggregation at each temperature is presented.

Circular Dichroism↗

PubMed2001

Effect of single mutations on the specificity of Escherichia coli FPG protein for excision of purine lesions from DNA damaged by free radicals.

The formamidopyrimidine N-DNA glycosylase (Fpg protein) of Escherichia coli is a DNA repair enzyme that is specific for the removal of purine-derived lesions from DNA damaged by free radicals and other oxidative processes. We investigated the effect of single mutations on the specificity of this enzyme for three purine-derived lesions in DNA damaged by free radicals. These damaging agents generate a multiplicity of base products in DNA, with the yields depending on the damaging agent. Wild type Fpg protein (wt-Fpg) removes 8-hydroxyguanine (8-OH-Gua), 4,6-diamino-5-formamidopyrimidine (FapyAde), and 2,6-diamino-4-hydroxy-5-formamidopyrimidine (FapyGua) from damaged DNA with similar specificities. We generated five mutant forms of this enzyme with mutations involving Lys-57-->Gly (FpgK57G), Lys-57-->Arg (FpgK57R), Lys-155-->Ala (FpgK155A), Pro-2-->Gly (FpgP2G), and Pro-2-->Glu (FpgP2E), and purified them to homogeneity. FpgK57G and FpgK57R were functional for removal of FapyAde and FapyGua with a reduced activity when compared with wt-Fpg. The removal of 8-OH-Gua was different in that the specificity of FpgK57G was significantly lower for its removal from irradiated DNA, whereas wt-Fpg, FpgK57G, and FpgK57R excised 8-OH-Gua from H2O2/Fe(III)-EDTA/ascorbic acid-treated DNA with almost the same specificity. FpgK155A and FpgP2G had very low activity and FpgP2E exhibited no activity at all. Michaelis-Menten kinetics of excision was measured and kinetic constants were obtained. The results indicate an important role of Lys-57 residue in the activity of Fpg protein for 8-OH-Gua, but a lesser significant role for formamidopyrimidines. Mutations involving Lys-155 and Pro-2 had a dramatic effect with Pro-2-->Glu leading to complete loss of activity, indicating a significant role of these residues. The results show that point mutations significantly change the specificity of Fpg protein and suggest that point mutations are also expected to change specificities of other DNA repair enzymes.

Ascorbic Acid↗

PubMed2001

The HAP1 protein stimulates the turnover of human mismatch-specific thymine-DNA-glycosylase to process 3,N(4)-ethenocytosine residues.

When present in DNA, 3,N(4)-ethenocytosine (epsilon C) residues are potentially mutagenic and carcinogenic in vivo. The enzymatic activity responsible for the repair of the epsilon C residues in human cells is the hTDG protein, the human thymine-DNA-glycosylase that removes thymine in a T/G base pair [Proc. Natl. Acad. Sci., U.S.A., 95 (1998) 8508]. One of the distinctive properties of the hTDG protein is that it remains tightly bound to the AP-site resulting from its glycosylase activity. In this paper we report that the human AP endonuclease, the HAP1 (Ape1, APEX Ref-1) protein, stimulates the processing of epsilon C residues by the hTDG protein in vitro, in a dose-dependent manner. This property of HAP1 protein is specific since E.coli Fpg, Nfo and Nth proteins, all endowed with an AP nicking activity, do not show similar features. The results suggest that the HAP1 protein displaces the hTDG protein bound to the AP-site and therefore increases the turnover of the hTDG protein. However, using a variety of techniques including gel retardation assay, surface plasmon resonance and two-hybrid system, it was not possible to detect evidence for a complex including the substrate, the hTDG and HAP1 proteins.

Binding Sites↗

PubMed2001

Recognition and kinetics for excision of a base lesion within clustered DNA damage by the Escherichia coli proteins Fpg and Nth.

Ionizing radiation and radiomimetic anticancer agents induce clustered DNA damages that are thought to lead to deleterious biological consequences, due to the challenge that clustered damage may present to the repair machinery of the cell. Specific oligonucleotides, containing either dihydrothymine (DHT) or 7,8-dihydro-8-oxoguanine (8-oxoG) opposite to specific lesions at defined positions on the complementary strand, have been used to determine the kinetic constants, K(M), k(cat), and specificity constants, for excision of DHT and 8-oxoG by the Escherichia coli base excision repair proteins, endonuclease III (Nth) and formamidopyrimidine glycosylase (Fpg), respectively. For excision of DHT opposite to 8-oxoadenine by Nth or Fpg proteins, or 8-oxoG opposite to 8-oxoG by Fpg, the major change in the specificity constant occurs when the second lesion on the complementary strand is one base to the site opposite to DHT or 8-oxoG. The specificity constants for excision of DHT or 8-oxoG by both proteins are reduced by up to 2 orders of magnitude when an abasic site or a strand break is opposite on the complementary strand. Whereas the values of K(M) are only slightly affected by the presence of a second lesion, the major change is seen as a reduction in the values of k(cat). The binding of Fpg protein to oligonucleotides containing 8-oxoG is inhibited, particularly when a single strand break is near to 8-oxoG on the complementary strand. It is inferred that not only the binding affinity of Fpg protein to the base lesion but also the rate of excision of the damaged base is reduced by the presence of another lesion, particularly a single strand break or an AP site on the complementary strand.

Apurinic Acid↗

PubMed2001

Frequencies and relative levels of clustered damages in DNA exposed to gamma rays in radioquenching vs. nonradioquenching conditions.

Clustered damage induced by ionizing radiation--two or more oxidized bases, abasic sites, or strand breaks within a few DNA helical turns--have been postulated to be major lethal and/or mutagenic sites. Although they have recently been shown to be induced in genomic DNAs by ionizing photons and particles, little is known of the factors that affect their yields or the relative levels of the classes of clusters. Toward this aim we have investigated the effect of DNA milieu, specifically, a nonradioquenching (phosphate) or radioquenching (Tris) solution, upon the generation of clustered lesions in a well-defined molecule, T7 bacteriophage DNA. Irradiation of DNA in Tris reduces the yields of all clustered damages to 1-3% of the levels formed in phosphate. Further, although the percentage of the total clusters in oxidized purine clusters is largely unchanged, and the level of abasic clusters decreases, the frequencies of double-strand breaks and oxidized pyrimidine clusters increase in the radioquenching solution. The ratio of the level of oxidized pyrimidine clusters to double-strand breaks in a DNA in radioquenching solution is similar to that obtained in DNA in human cells, also a radioquenching environment.

Bacteriophage T7↗

PubMed2001

Clustered DNA damages as dosemeters for ionising radiation exposure and biological responses.

Clustered DNA damages--two or more lesions (oxidised bases. abasic sites, or strand breaks) within a few DNA helical turns on opposing strands--are induced in DNA in solution and in vivo in human cells by ionising radiation. They have been postulated to be difficult to repair, and thus of potentially high biological significance. Since the total of clustered damages produced by ionising radiation is at about 3 to 4 times higher levels than double-strand breaks and are apparently absent in unirradiated cells, levels of clustered damages present immediately alter radiation exposure could serve as sensitive dosemeters of radiation exposure. Since some clusters may not be repairable and may accumulate in cells, they might also be useful as integrating dosemeters of biological effects of radiation damage.

DNA↗

PubMed2001

Clustered DNA damages induced by high and low LET radiation, including heavy ions.

Clustered DNA damages--here defined as two or more lesions (strand breaks, oxidized purines, oxidized pyrimidines or abasic sites) within a few helical turns--have been postulated as difficult to repair accurately, and thus highly significant biological lesions. Further, attempted repair of clusters may produce double strand breaks (DSBs). However, until recently, there was no way to measure ionizing radiation-induced clustered damages, except DSB. We recently described an approach for measuring classes of clustered damages (oxidized purine clusters, oxidized pyrimidine clusters, abasic clusters, along with DSB). We showed that ionizing radiation (gamma rays and Fe ions, 1 GeV/amu) does induce such clusters in genomic DNA in solution and in human cells. These studies also showed that each damage cluster results from one radiation hit (and its track), thus indicating that they can be induced by very low doses of radiation, i.e. two independent hits are not required for cluster induction. Further, among all complex damages, double strand breaks comprise--at most-- ~20%, with the other clustered damages being at least 80%.

Cells, Cultured↗

PubMed2000

Fusion of chromatophores from photosynthetic bacteria with a supported lipid layer: characterization of the electric units.

Direct electrometric measurements of membrane potential changes are a valuable tool for study of vectorial transfer of electrons, protons, and ions. Commonly model membrane systems are created by fusion of lipid/protein vesicles with lipid-coated thin films. We characterized the electric units resulting from this process using chromatophores from the purple bacterium Rhodobacter sphaeroides and either a Mylar film or a planar modified gold electrode as support. Investigation of the shunting activity of the ionophore gramicidin on the flash-induced potential change demonstrates fusion of individual chromatophores to form independent 'blisters', which preserve an interior aqueous compartment. Under current-clamp conditions the photovoltage follows the change of the membrane potential of the individual blisters.

Bacterial Chromatophores↗

PubMed2000

AlkA protein is the third Escherichia coli DNA repair protein excising a ring fragmentation product of thymine.

Various forms of oxidative stress lead to the formation of damaged bases including N-(2-deoxy-beta-D-erythro-pentofuranosyl)-N-3-(2R-hydroxyisobutyric acid)-urea or alphaRT, the fragmentation product of thymine formed from 5R-thymidine C5-hydrate upon hydrolysis. It was shown that alphaRT is excised by Escherichia coli Fpg and Nth proteins. Here we report that when present in DNA, alphaRT is, in addition, a substrate for the E. coli AlkA protein with an apparent K(m) value of congruent with170 nM. alphaRT positioned opposite T, dG, dC, and dA were efficiently excised by AlkA protein from duplex oligodeoxynucleotides in the following order: dA approximately T >> dC approximately dG. This is the first example of the excision of a ring opened form of a pyrimidine by AlkA protein and also the first example where the same DNA base lesion is excised by three different DNA glycosylases of the base excision repair pathway. The present results suggest possible structural similarity of the active site between E. coli AlkA, Fpg, and Nth proteins.

5' Untranslated Regions↗

PubMed2000

Comparison of the levels of 8-hydroxyguanine in DNA as measured by gas chromatography mass spectrometry following hydrolysis of DNA by Escherichia coli Fpg protein or formic acid.

8-hydroxyguanine (8-OH-Gua) is one of many lesions generated in DNA by oxidative processes including free radicals. It is the most extensively investigated lesion, due to its miscoding properties and its potential role in mutagenesis, carcinogenesis and aging, and also to the existence of analytical methods using HPLC and gas chromatography mass spectrometry (GC/MS). Some studies raised the possibility of artifacts generated during sample preparation. We investigated several experimental conditions in order to eliminate possible artifacts during the measurement of 8-OH-Gua by GC/MS. Derivatization has been reported to produce artifacts by oxidation of guanine to 8-OH-Gua in acid-hydrolysates of DNA, although the extent of artifacts seems to depend on experimental conditions. For removal of 8-OH-Gua from DNA, we used either formic acid hydrolysis or specific enzymatic hydrolysis with Escherichia coli Fpg protein. Derivatization of enzyme-hydrolysates should not generate additional 8-OH-Gua because of the absence of guanine, which is not released by the enzyme, whereas guanine released by acid may be oxidized to yield 8-OH-Gua. The measurement of 8-OH-Gua in calf thymus DNA by GC/isotope-dilution MS (GC/IDMS) using these two different hydrolyses yielded similar levels of 8-OH-Gua. This indicated that no artifacts occurred during derivatization of acid-hydrolysates of DNA. Pyridine instead of acetonitrile and room temperature were used during derivatization. Pyridine reduced the level of 8-OH-Gua, when compared with acetonitrile, indicating its potential to prevent oxidation. Two different stable-isotope labeled analogs of 8-OH-Gua used as internal standards for GC/IDMS analysis yielded similar results. A comparison of the present results with the results of recent trials by the European Standards Committee for Oxidative DNA Damage (ESCODD) is also presented.

Animals↗

PubMed2000

Clustered damages and total lesions induced in DNA by ionizing radiation: oxidized bases and strand breaks.

Ionizing radiation induces both isolated DNA lesions and clustered damages-multiple closely spaced lesions (strand breaks, oxidized purines, oxidized pyrimidines, or abasic sites within a few helical turns). Such clusters are postulated to be difficult to repair and thus potentially lethal or mutagenic lesions. Using highly purified enzymes that cleave DNA at specific classes of damage and electrophoretic assays developed for quantifying isolated and clustered damages in high molecular length genomic DNAs, we determined the relative frequencies of total lesions and of clustered damages involving both strands, and the composition and origin of such clusters. The relative frequency of isolated vs clustered damages depends on the identity of the lesion, with approximately 15-18% of oxidized purines, pyrimidines, or abasic sites in clusters recognized by Fpg, Nth, or Nfo proteins, respectively, but only about half that level of frank single strand breaks in double strand breaks. Oxidized base clusters and abasic site clusters constitute about 80% of complex damages, while double strand breaks comprise only approximately 20% of the total. The data also show that each cluster results from a single radiation (track) event, and thus clusters will be formed at low as well as high radiation doses.

DNA↗

PubMed2000

Novel substrates of Escherichia coli nth protein and its kinetics for excision of modified bases from DNA damaged by free radicals.

Escherichia coli Nth protein (endonuclease III) is a DNA glycosylase with a broad substrate specificity for pyrimidine derivatives. We discovered novel substrates of E. coli Nth protein using gas chromatography/isotope-dilution mass spectrometry and DNA samples, which were damaged by gamma-irradiation or by H(2)O(2)/Fe(III)-EDTA/ascorbic acid. These were 4, 6-diamino-5-formamidopyrimidine, 5,6-dihydroxyuracil, and 5, 6-dihydroxycytosine. The first compound was recognized for the first time as a purine-derived substrate of the enzyme. We also investigated kinetics of excision of a multitude of modified bases from three damaged DNA substrates. Excision of modified bases was determined as a function of enzyme concentration, incubation time, and substrate concentration. Excision followed Michaelis-Menten kinetics. Kinetic parameters were determined for the following modified bases: 4,6-diamino-5-formamidopyrimidine, cis- and trans-thymine glycols, 5-hydroxycytosine, cis- and trans-uracil glycols, 5-hydroxyuracil, 5-hydroxy-5-methylhydantoin, alloxan, 5, 6-dihydroxycytosine, 5,6-dihydroxyuracil, 5-hydroxy-6-hydrothymine, and 5-hydroxy-6-hydrouracil. The results show that three newly discovered substrates were excised by the enzyme with a preference similar to excision of its known major substrates such as thymine glycol and 5-hydroxycytosine. Excision kinetics significantly depended on the nature of the damaged DNA substrates in agreement with previous results on other DNA glycosylases. Specificity constants (k(cat)/K(M)) of E. coli Nth protein were compared to those of its previously investigated functional homologues such as human and Schizosaccharomyces pombe Nth proteins and Saccharomyces cerevisiae Ntg1 and Ntg2 proteins. This comparison shows that significant differences exist with respect to substrate specificity and kinetic parameters despite extensive structural conservation among the Nth homologues.

Bacterial Proteins↗

PubMed2000

Clustered DNA damage, influence on damage excision by XRS5 nuclear extracts and Escherichia coli Nth and Fpg proteins.

Ionizing radiation and radiomimetic anticancer agents induce clustered DNA damage, which are thought to reflect the biological severity. Escherichia coli Nth and Fpg and nuclear extracts from XRS5, a Chinese hamster ovary Ku-deficient cell line, have been used to study the influence on their substrate recognition by the presence of a neighboring damage or an abasic site on the opposite strand, as models of clustered DNA damage. These proteins were tested for their efficiency to induce a single-strand break on a (32)P-labeled oligonucleotide containing either an abasic (AP) site, dihydrothymine (DHT), 7,8-dihydro-8-oxo-2'deoxyguanine, or 7, 8-dihydro-8-oxo-2'deoxyadenine at positions 1, 3, or 5 base pairs 5' or 3' to either an AP site or DHT on the labeled strand. DHT excision is much more affected than cleavage of an AP site by the presence of other damage. The effect on DHT excision is greatest with a neighboring AP site, with the effect being asymmetric with Nth and Fpg. Therefore, this large inhibition of the excision of DHT by the presence of an opposite AP site may minimize the formation of double-strand breaks in the processing of DNA clustered damages.

8-Hydroxy-2'-Deoxyguanosine↗

PubMed2000

Role of the N-terminal proline residue in the catalytic activities of the Escherichia coli Fpg protein.

The Escherichia coli Fpg protein is a DNA glycosylase/AP lyase. It removes, in DNA, oxidized purine residues, including the highly mutagenic C8-oxo-guanine (8-oxoG). The catalytic mechanism is believed to involve the formation of a transient Schiff base intermediate formed between DNA containing an oxidized residue and the N-terminal proline of the Fpg protein. The importance and the role of this proline upon the various catalytic activities of the Fpg protein was examined by targeted mutagenesis, resulting in the construction of three mutant Fpg proteins: Pro-2 --> Gly (FpgP2G), Pro-2 --> Thr (FpgP2T), and Pro-2 --> Glu (FpgP2E). The formamidopyrimidine DNA glycosylase activities of FpgP2G and FpgP2T were comparable and accounted for 10% of the wild-type activity. FpgP2G and FpgP2T had barely detectable 8-oxoG-DNA glycosylase activity and produced minute Schiff base complex with 8-oxoG/C DNA. FpgP2G and FpgP2T mutants did not cleave a DNA containing preformed AP site but readily produced Schiff base complex with this substrate. FpgP2E was completely inactive in all the assays. The binding constants of the different mutants when challenged with a duplex DNA containing a tetrahydrofuran residue were comparable. The mutant Fpg proteins barely or did not complement in vivo the spontaneous transitions G/C --> T/A in E. coli BH990 (fpg mutY) cells. These results show the mandatory role of N-terminal proline in the 8-oxoG-DNA glycosylase activity of the Fpg protein in vitro and in vivo as well as in its AP lyase activity upon preformed AP site but less in the 2,6-diamino-4-hydroxy-5-N-methylformamidopyrimidine-DNA glycosylase activity.

Amino Acid Substitution↗

PubMed2000

Interactions of the human, rat, Saccharomyces cerevisiae and Escherichia coli 3-methyladenine-DNA glycosylases with DNA containing dIMP residues.

In DNA, the deamination of dAMP generates 2'-deoxy-inosine 5'-monophosphate (dIMP). Hypoxanthine (HX) residues are mutagenic since they give rise to A.T-->G.C transition. They are excised, although with different efficiencies, by an activity of the 3-methyl-adenine (3-meAde)-DNA glycosylases from Escherichia coli (AlkA protein), human cells (ANPG protein), rat cells (APDG protein) and yeast (MAG protein). Comparison of the kinetic constants for the excision of HX residues by the four enzymes shows that the E.coli and yeast enzymes are quite inefficient, whereas for the ANPG and the APDG proteins they repair the HX residues with an efficiency comparable to that of alkylated bases, which are believed to be the primary substrates of these DNA glycosylases. Since the use of various substrates to monitor the activity of HX-DNA glycosylases has generated conflicting results, the efficacy of the four 3-meAde-DNA glycosylases of different origin was compared using three different substrates. Moreover, using oligo-nucleotides containing a single dIMP residue, we investigated a putative sequence specificity of the enzymes involving the bases next to the HX residue. We found up to 2-5-fold difference in the rates of HX excision between the various sequences of the oligonucleotides studied. When the dIMP residue was placed opposite to each of the four bases, a preferential recognition of dI:T over dI:dG, dI:dC and dI:dA mismatches was observed for both human (ANPG) and E.coli (AlkA) proteins. At variance, the yeast MAG protein removed more efficiently HX from a dI:dG over dI:dC, dI:T and dI:dA mismatches.

Animals↗

PubMed2000

Clustered DNA damages induced in isolated DNA and in human cells by low doses of ionizing radiation.

Clustered DNA damages-two or more closely spaced damages (strand breaks, abasic sites, or oxidized bases) on opposing strands-are suspects as critical lesions producing lethal and mutagenic effects of ionizing radiation. However, as a result of the lack of methods for measuring damage clusters induced by ionizing radiation in genomic DNA, neither the frequencies of their production by physiological doses of radiation, nor their repairability, nor their biological effects are known. On the basis of methods that we developed for quantitating damages in large DNAs, we have devised and validated a way of measuring ionizing radiation-induced clustered lesions in genomic DNA, including DNA from human cells. DNA is treated with an endonuclease that induces a single-strand cleavage at an oxidized base or abasic site. If there are two closely spaced damages on opposing strands, such cleavage will reduce the size of the DNA on a nondenaturing gel. We show that ionizing radiation does induce clustered DNA damages containing abasic sites, oxidized purines, or oxidized pyrimidines. Further, the frequency of each of these cluster classes is comparable to that of frank double-strand breaks; among all complex damages induced by ionizing radiation, double-strand breaks are only about 20%, with other clustered damage constituting some 80%. We also show that even low doses (0.1-1 Gy) of high linear energy transfer ionizing radiation induce clustered damages in human cells.

Bacteriophage T7↗

PubMed1999

Substrate specificity of Deinococcus radiodurans Fpg protein.

A DNA repair enzyme has recently been isolated from the ionizing radiation-resistant bacterium Deinococcus radiodurans [Bauche, C., and Laval, J. (1999) J. Bacteriol. 181, 262-269]. This enzyme is a homologue of the Fpg protein of Escherichia coli. We investigated the substrate specificity of this enzyme for products of oxidative DNA base damage using gas chromatography/isotope-dilution mass spectrometry and DNA substrates, which were either gamma-irradiated or treated with H(2)O(2)/Fe(III)-EDTA/ascorbic acid. Excision of purine lesions 2,6-diamino-4-hydroxy-5-formamidopyrimidine (FapyGua), 4,6-diamino-5-formamidopyrimidine (FapyAde), and 8-hydroxyguanine (8-OH-Gua) was observed among 17 lesions detected in damaged DNA substrates. The extent of excision was determined as a function of enzyme concentration, time, and substrate concentration. FapyGua and FapyAde were excised with similar specificities from three DNA substrates, whereas 8-OH-Gua was the least preferred lesion. The results show that D. radiodurans Fpg protein and its homologue E. coli Fpg protein excise the same modified DNA bases, but the excision rates of these enzymes are significantly different. Formamidopyrimidines are preferred substrates of D. radiodurans Fpg protein over 8-OH-Gua, whereas E. coli Fpg protein excises these three lesions with similar efficiencies from various DNA substrates. Substrate specificities of these enzymes were also compared with that of Saccharomyces cerevisiae Ogg1 protein, which excises FapyGua and 8-OH-Gua, but not FapyAde.

DNA↗

PubMed1999

The type of DNA glycosylase determines the base excision repair pathway in mammalian cells.

The base excision repair (BER) of modified nucleotides is initiated by damage-specific DNA glycosylases. The repair of the resulting apurinic/apyrimidinic site involves the replacement of either a single nucleotide (short patch BER) or of several nucleotides (long patch BER). The mechanism that controls the selection of either BER pathway is unknown. We tested the hypothesis that the type of base damage present on DNA, by determining the specific DNA glycosylase in charge of its excision, drives the repair of the resulting abasic site intermediate to either BER branch. In mammalian cells hypoxanthine (HX) and 1,N6-ethenoadenine (epsilonA) are both substrates for the monofunctional 3-methyladenine DNA glycosylase, the ANPG protein, whereas 7,8-dihydro-8-oxoguanine (8-oxoG) is removed by the bifunctional DNA glycosylase/beta-lyase 8-oxoG-DNA gly- cosylase (OGG1). Circular plasmid molecules containing a single HX, epsilonA, or 8-oxoG were constructed. In vitro repair assays with HeLa cell extracts revealed that HX and epsilonA are repaired via both short and long patch BER, whereas 8-oxoG is repaired mainly via the short patch pathway. The preferential repair of 8-oxoG by short patch BER was confirmed by the low efficiency of repair of this lesion by DNA polymerase beta-deficient mouse cells as compared with their wild-type counterpart. These data fit into a model where the intrinsic properties of the DNA glycosylase that recognizes the lesion selects the branch of BER that will restore the intact DNA template.

Adenine↗