Repair Pathways for Processing of 8-Oxoguanine in DNA by Mammalian Cell Extracts

The repair pathways involved in the removal of 8-oxo-7,8-dihydroguanine (8-oxoguanine) in DNA by mammalian cell extracts have been examined. Closed circular DNA constructs containing a single 8-oxoguanine at a defined site were used as substrates to determine the patch size generated after in vitro repair by mammalian cell extracts. Restriction analysis of the repair incorporation in the vicinity of the lesion indicated that up to 75% of the 8-oxoguanine was repaired via the single nucleotide replacement mechanism in both human and mouse cell extracts. Approximately 25% of the 8-oxoguanine lesions were repaired by the long patch repair pathway. Repair incorporation 5′ to the lesion, characteristic for nucleotide excision repair, was not significant. Elimination of the DNA polymerase β (polβ)-dependent single nucleotide base excision repair pathway in extracts prepared from polβ-deficient mouse cells resulted in extension of the repair gap to 4–5 nucleotides 3′ to the lesion in 50% of the repair events, suggesting the increased involvement of the long patch repair pathway. However, about one-half of the 8-oxoguanine repair was still accomplished through replacement of only one nucleotide in the polβ-deficient cell extracts. These data indicate the existence of an alternative polβ-independent single nucleotide repair patch pathway for processing of 8-oxoguanine in DNA. The repair pathways involved in the removal of 8-oxo-7,8-dihydroguanine (8-oxoguanine) in DNA by mammalian cell extracts have been examined. Closed circular DNA constructs containing a single 8-oxoguanine at a defined site were used as substrates to determine the patch size generated after in vitro repair by mammalian cell extracts. Restriction analysis of the repair incorporation in the vicinity of the lesion indicated that up to 75% of the 8-oxoguanine was repaired via the single nucleotide replacement mechanism in both human and mouse cell extracts. Approximately 25% of the 8-oxoguanine lesions were repaired by the long patch repair pathway. Repair incorporation 5′ to the lesion, characteristic for nucleotide excision repair, was not significant. Elimination of the DNA polymerase β (polβ)-dependent single nucleotide base excision repair pathway in extracts prepared from polβ-deficient mouse cells resulted in extension of the repair gap to 4–5 nucleotides 3′ to the lesion in 50% of the repair events, suggesting the increased involvement of the long patch repair pathway. However, about one-half of the 8-oxoguanine repair was still accomplished through replacement of only one nucleotide in the polβ-deficient cell extracts. These data indicate the existence of an alternative polβ-independent single nucleotide repair patch pathway for processing of 8-oxoguanine in DNA. In living cells reactive oxygen species are formed continuously as a consequence of normal cellular metabolism and are also generated by a number of external factors. The reaction of active oxygen species with DNA results in numerous forms of base damage, and 8-oxoguanine 1The abbreviations used are: 8-oxoguanine, 8-oxo-7,8-dihydroguanine; NER, nucleotide excision repair; BER, base excision repair; AP sites, apurinic/apyrimidinic sites, abasic sites; PCNA, proliferating cell nuclear antigen; bp, base pair(s); polβ, DNA polymerase β; polδ, DNA polymerase δ; hOGG1, human 8-oxoguanine-DNA glycosylase; bp, base pair; XP-A, xeroderma pigmentosum group A. is one of the most abundant lesions generated. An increased level of 8-oxoguanine has been observed after treatment of cells with UV, ionizing irradiation or chemical mutagens that generate oxygen radicals (for review, see Ref.1Demple B. Harrison L. Annu. Rev. Biochem. 1994; 63: 915-948Crossref PubMed Scopus (1300) Google Scholar). Although many different lesions are formed in DNA after oxidative stress, 8-oxoguanine is one of the most significant and the most studied lesions. 8-Oxoguanine in a syn conformation can base pair with adenine and induce transversion mutations (2Shibutani S. Takeshita M. Grollman A.P. Nature. 1991; 349: 431-434Crossref PubMed Scopus (2047) Google Scholar, 3Maki H. Sekiguchi M. Nature. 1992; 355: 273-275Crossref PubMed Scopus (792) Google Scholar). This demonstrated mutagenic potential is thought to be involved in cancer and aging (4Ames B.N. Free Radical Res. Commun. 1989; 7: 121-128Crossref PubMed Scopus (626) Google Scholar, 5Ames B.N. Gold L.S. Mutat. Res. 1991; 250: 3-16Crossref PubMed Scopus (686) Google Scholar, 6Ames B.N. Shigenaga M.K. Hagen T.M. Proc. Natl. Acad. Sci. U. S. A. 1993; 90: 7915-7922Crossref PubMed Scopus (5446) Google Scholar, 7Fraga C.G. Shigenaga M.K. Park J.-W. Degan P. Ames B.N. Proc. Natl. Acad. Sci. U. S. A. 1990; 87: 4533-4537Crossref PubMed Scopus (993) Google Scholar, 8Lindahl T. Nature. 1993; 362: 709-715Crossref PubMed Scopus (4378) Google Scholar). To avoid deleterious consequences, 8-oxoguanine must be efficiently removed from DNA. Based on previous studies in bacterial cells it has been established that base excision repair (BER) is the major pathway for the removal of this lesion (8Lindahl T. Nature. 1993; 362: 709-715Crossref PubMed Scopus (4378) Google Scholar). Recently human 8-oxoguanine-DNA glycosylase (hOGG1) has been cloned and purified by several groups (9Radicella J.P. Dherin C. Desmaze C. Fox M.S. Boiteux S. Proc. Natl. Acad. Sci. U. S. A. 1997; 94: 8010-8015Crossref PubMed Scopus (571) Google Scholar, 10Roldan-Arjona T. Wei Y.F. Carter K.C. Klungland A. Anselmino C. Wang R.P. Augustus M. Lindahl T. Proc. Natl. Acad. Sci. U. S. A. 1997; 94: 8016-8020Crossref PubMed Scopus (342) Google Scholar, 11Rosenquist T.A. Zharkov D.O. Grollman A.P. Proc. Natl. Acad. Sci. U. S. A. 1997; 94: 7429-7434Crossref PubMed Scopus (459) Google Scholar), thus providing an enzymatic basis for the involvement of BER in removal of this lesion in mammalian cells. There are two pathways for base excision repair involving different subsets of proteins and operating independently (12Matsumoto Y. Kim K. Bogenhagen D.F. Mol. Cell. Biol. 1994; 14: 6187-6197Crossref PubMed Scopus (262) Google Scholar, 13Frosina G. Fortini P. Rossi O. Carrozzino F. Raspaglio G. Cox L.S. Lane D.P. Abbondandolo A. Dogliotti E. J. Biol. Chem. 1996; 271: 9573-9578Abstract Full Text Full Text PDF PubMed Scopus (449) Google Scholar, 14Klungland A. Lindahl T. EMBO J. 1997; 16: 3341-3348Crossref PubMed Scopus (666) Google Scholar). Both pathways are initiated by DNA glycosylases that recognize and remove the damaged base leaving an abasic site (AP site). The AP site is recognized by AP endonuclease, which introduces a DNA strand break 5′ to the baseless sugar, and then DNA polymerase β (polβ) catalyzes β elimination of the 5′ sugar phosphate residue and fills the one nucleotide gap. The nick is then sealed by DNA ligase (14Klungland A. Lindahl T. EMBO J. 1997; 16: 3341-3348Crossref PubMed Scopus (666) Google Scholar). In polβ-deficient cell extracts this repair mechanism is disrupted and the PCNA-dependent pathway then become the major mode of base excision repair (16Biade S. Sobol R.W. Wilson S.H. Matsumoto Y. J. Biol. Chem. 1998; 273: 898-902Abstract Full Text Full Text PDF PubMed Scopus (179) Google Scholar, 17Fortini P. Pascucci B. Parlanti E. Sobol R.W. Wilson S.H. Dogliotti E. Biochemistry. 1998; 37: 3575-3580Crossref PubMed Scopus (200) Google Scholar). 2G. Dianov, C. Bischoff, J. Piotrovski, and V. A. Bohr, submitted for publication. The proliferating cell nuclear antigen (PCNA)-dependent pathway, in addition to DNA glycosylase and AP endonuclease, also involves flap endonuclease, PCNA, DNA polymerase δ, and DNA ligase (14Klungland A. Lindahl T. EMBO J. 1997; 16: 3341-3348Crossref PubMed Scopus (666) Google Scholar). Neither of these enzymes can remove a 5′ sugar phosphate and generate a 1-nucleotide gap. To remove the 5′ sugar phosphate, DNA polymerase first adds several nucleotides to the 3′ end of the nick and exposes the 5′ sugar phosphate as part of a single-stranded flap structure. This flap structure is recognized and excised by flap endonuclease, and the DNA is finally ligated by DNA ligase (14Klungland A. Lindahl T. EMBO J. 1997; 16: 3341-3348Crossref PubMed Scopus (666) Google Scholar). These repair events result in a 2–5-nucleotide-long repair patch (13Frosina G. Fortini P. Rossi O. Carrozzino F. Raspaglio G. Cox L.S. Lane D.P. Abbondandolo A. Dogliotti E. J. Biol. Chem. 1996; 271: 9573-9578Abstract Full Text Full Text PDF PubMed Scopus (449) Google Scholar). In this reaction, PCNA and probably replication factor C assist in loading the DNA polymerase onto DNA (18Podust L.P. Podust V.N. Floth C. Hubscher U. Nucleic Acids Res. 1994; 22: 2970-2975Crossref PubMed Scopus (53) Google Scholar) and also stimulate the endonuclease flap endonuclease (19Li X. Li J. Harrington J. Lieber M.R. Burgers P.M.J. J. Biol. Chem. 1995; 270: 22109-22112Crossref PubMed Scopus (254) Google Scholar). The role of BER pathways has been characterized for the repair of uracil and AP sites (12Matsumoto Y. Kim K. Bogenhagen D.F. Mol. Cell. Biol. 1994; 14: 6187-6197Crossref PubMed Scopus (262) Google Scholar, 13Frosina G. Fortini P. Rossi O. Carrozzino F. Raspaglio G. Cox L.S. Lane D.P. Abbondandolo A. Dogliotti E. J. Biol. Chem. 1996; 271: 9573-9578Abstract Full Text Full Text PDF PubMed Scopus (449) Google Scholar, 14Klungland A. Lindahl T. EMBO J. 1997; 16: 3341-3348Crossref PubMed Scopus (666) Google Scholar, 20Dianov G. Lindahl T. Curr. Biol. 1994; 4: 1069-1076Abstract Full Text Full Text PDF PubMed Scopus (217) Google Scholar, 21Kubota Y. Nash R.A. Klungland A. Schar P. Barnes D. Lindahl T. EMBO J. 1996; 15: 6662-6670Crossref PubMed Scopus (693) Google Scholar, 22Prasad R. Singhal R.K. Srivastava D.K. Molina J.T. Tomkinson A.E. Wilson S.H. J. Biol. Chem. 1996; 271: 16000-16007Abstract Full Text Full Text PDF PubMed Scopus (230) Google Scholar), but there are no studies on the detailed pathways for the removal of 8-oxoguanine. The processing of 8-oxoguanine may be different from that of uracil or AP sites for several reasons. First, 8-oxoguanine-DNA glycosylase unlike uracil-DNA glycosylase has an intrinsic AP lyase activity, and this raises the possibility for the existence of an alternative BER pathway independent of the AP lyase activity of DNA polymerase β. Second, it has recently been observed that 8-oxoguanine is recognized and processed by the human nucleotide excision repair (NER) system, proposing a role for in removal of this lesion J.T. T. A. Proc. Natl. Acad. Sci. U. S. A. 1997; 94: PubMed Scopus Google Scholar). To the pathways involved in the repair of 8-oxoguanine, have used a DNA containing a single 8-oxoguanine lesion at a defined have the role of and PCNA-dependent BER pathways as as that of the pathway in the removal of this lesion in mammalian cell extracts. The repair incorporation was in the vicinity of the lesion, and the number and of nucleotides were to determine the repair via the single nucleotide pathway, via the PCNA-dependent BER pathway, or through the The repair incorporation was also in extracts prepared from cells to the role of the polβ-independent pathways in the removal of 8-oxoguanine in DNA. In this that the single nucleotide repair patch BER pathway is the mechanism for processing of 8-oxoguanine by mammalian cell extracts. also for the existence of a polβ-independent single nucleotide repair patch pathway for removal of 8-oxoguanine in DNA. cells and pigmentosum group cells were from the were in the by the DNA polymerase β mouse and cell were from S. H. Wilson and were as R.W. R. H. Singhal R.K. R. K. Wilson S.H. Nature. 1996; PubMed Scopus Google Scholar). used were from and The DNA to the was cloned site of DNA. The single-stranded was and the was by circular DNA containing a single lesion was by of single-stranded DNA with a of the for the single 8-oxoguanine and with for the The reaction containing and of DNA of DNA and of enzymes from was for at Closed circular DNA was by purified by and by in a DNA substrates were at in and The of a single 8-oxoguanine was by of to was in a containing and for at was by A. cell extracts were prepared from of cells by the of A. M. P. PubMed Scopus Google Scholar). repair of single of of and of and of a cell the reaction was with both and the of was also to were at for the reaction, DNA was purified from the reaction by and and with of the indicated endonuclease for in a by the were in a and the was in of and 50% for at and on a containing and The of was on a An containing sites for analysis of DNA repair incorporation in the vicinity of the lesion was cloned in DNA. DNA was by single-stranded DNA with an and DNA was purified by The DNA a 8-oxoguanine lesion and sites for analysis of repair patch size To the of the lesion, demonstrated that DNA is to the bacterial that 8-oxoguanine in DNA and the 5′ and 3′ to the lesion J. H. S. J. Grollman A.P. S. Proc. Natl. Acad. Sci. U. S. A. 1991; PubMed Scopus (693) Google Scholar). The of the DNA two a containing the lesion and a the of the DNA. The were then 3′ with DNA polymerase The of the of the generated a DNA in both and containing 8-oxoguanine in only one of The DNA was then with The of the at the site of 8-oxoguanine generate a The result of the is in A. There are no sites in the and the is observed only in DNA. both DNA were and only one of the lesion, the of the of the of in the and that at of the DNA single 8-oxoguanine at the defined of DNA. of 8-oxoguanine DNA with or DNA was with endonuclease, by end with DNA polymerase with of for at and by on a repair incorporation the of and DNA with human cell of DNA was with of cell from the human cell in the of for at The DNA was from the reaction with and repair incorporation was after on a The repair of 8-oxoguanine was in the DNA repair incorporation DNA containing 8-oxoguanine or prepared by the but containing a normal base pair at the were with human cell extracts in the of for DNA repair, the DNA was purified from the reaction with endonuclease, and by The reaction with a that an 8-oxoguanine residue in DNA. The analysis of the in indicated that after with human cell extracts incorporation in both damaged and DNA constructs at the of the However, to the the incorporation the was incorporation the of the The incorporation the was or no incorporation was in the of the DNA. The incorporation of the also that repair of 8-oxoguanine was by the cell not of that were not To the size of the repair patch in human a of repaired DNA and This a that the 8-oxoguanine residue in a that nucleotides and a nucleotides 3′ to the single nucleotide repair patch be by incorporation in the and extension of the repair patch result in the of the or The of the incorporation in the that of the incorporation the was in the and 25% of the incorporation was in the and the incorporation was to the number of potential sites for incorporation in the two in the and one in the that of the repair incorporation was in the were in which incorporation of both and was in the repair The nucleotide 3′ to the 8-oxoguanine and from nucleotides In these incorporation of these nucleotides 3′ to the 8-oxoguanine was these results were to the number of potential sites for and of the incorporation was in the that a single nucleotide repair patch is the major pathway for the repair of 8-oxoguanine in human cell extracts. data were and are in incorporation in the vicinity of cell cell results of analysis of an in vitro repaired DNA were with and the incorporation was to the number of potential sites for An of independent is in a The results of analysis of an in vitro repaired DNA were with and the incorporation was to the number of potential sites for An of independent is To the role of the polβ-independent pathways in the repair of 8-oxoguanine from the repair of this lesion in extracts prepared from mouse cells and from cells The DNA containing a single 8-oxoguanine residue was with these and then with incorporation was in the from the DNA repaired in normal and polβ-deficient cell extracts incorporation was in the cell extracts in cell extracts at of the The analysis of repair patch size by with and was as for human cell extracts. The incorporation of and was in these repair of DNA in cell extracts prepared from normal mouse of the incorporation was in the This as was for human cell mouse cell extracts repair 8-oxoguanine via the single nucleotide repair patch pathway. In the extracts the repair gap most was by and incorporation in the and was However, the from DNA repaired in extracts up to of the suggesting that a part of the repair in these extracts was accomplished through a single nucleotide gap. The of incorporation in the observed in several independent with and mouse extracts is in level of incorporation the that an polβ-independent repair pathway a 1-nucleotide repair patch is involved in the repair of 8-oxoguanine in a polβ-deficient cell extracts. Recently it has been that in human cell extracts the pathway is involved in the repair of 8-oxoguanine in DNA J.T. T. A. Proc. Natl. Acad. Sci. U. S. A. 1997; 94: PubMed Scopus Google Scholar). the of BER and in the repair of 8-oxoguanine in DNA. base excision repair, the AP lyase activity of the glycosylase or a AP endonuclease the to the The DNA repair events result in the replacement of one or nucleotides 3′ to the In NER, the nucleotides 5′ and nucleotides 3′ to the damaged site A. Annu. Rev. Biochem. 1996; PubMed Scopus Google J. Biol. Chem. 1997; PubMed Scopus Google Scholar). the of the be in vitro The and incorporation this to the incorporation the the of to the repair of 8-oxoguanine in the cell There are two sites to the 8-oxoguanine, with two independent of of these and was used to incorporation 5′ to the that only of the incorporation the was to incorporation the this incorporation activity on the 8-oxoguanine lesion, it after repair in cell extracts from To incorporation the after repair of DNA in a cell was observed a in incorporation the after the repair reaction in the extracts but there were no in the incorporation the with the incorporation the also the role for the major BER pathway is The with normal and polβ-deficient mouse cell extracts were as for human cell extracts. in the incorporation in the in the polβ-deficient cell extracts were with the normal cell extracts These data that the role of in repair of 8-oxoguanine is not increased in polβ-deficient cell extracts. have the involvement of different repair pathways in the processing of 8-oxoguanine in mammalian cell extracts analysis of in vitro repaired DNA. the that the gap size long patch repair events is at 4–5 nucleotides and that repair incorporation is independent of the nucleotide at and 3′ to the analysis have the repair incorporation in the first nucleotides 3′ to the 8-oxoguanine. The data on repair incorporation in the vicinity of 8-oxoguanine are in These data are to the number of potential sites for the and However, to be in of a of the different pathways to repair of 8-oxoguanine, these data be the is not only the of a 1-nucleotide gap but also repair of to the of a single nucleotide repair pathway, the long patch of incorporation the be the incorporation in the was from the incorporation in the that of a repair events were accomplished through a single nucleotide repair thus that in cell extracts this pathway is the pathway for the repair of 8-oxoguanine in DNA. The pathways to the repair of the of the 8-oxoguanine. The data on the of BER pathways to the processing of 8-oxoguanine by human cell extracts are in These data are in with a previous from this that pathways are involved in the repair of 8-oxoguanine in damaged DNA M. Nucleic Acids Res. 1998; PubMed Scopus Google Scholar). the involvement of in the removal of 8-oxoguanine has been J.T. T. A. Proc. Natl. Acad. Sci. U. S. A. 1997; 94: PubMed Scopus Google Scholar). have the of BER and in the repair of this lesion in mammalian cell extracts. Although vitro repair have used in is for both BER and NER, were to see significant involvement of in the removal of 8-oxoguanine in cell extracts or in cell extracts prepared from in which the major pathway for base excision repair is The excision used by J.T. T. A. Proc. Natl. Acad. Sci. U. S. A. 1997; 94: PubMed Scopus Google Scholar) was to only activity, the of was in repair of 8-oxoguanine. In and BER for the and the BER is the pathway for repair of 8-oxoguanine, it is in processing 8-oxoguanine. not a role for in the repair of oxidative DNA may as a the major BER pathways are is for repair, and repair of in DNA has been demonstrated recently T. 1997; PubMed Scopus Google Scholar). observed a of repair incorporation in the The to DNA and is involved in DNA and processing J. Biol. Chem. 1997; PubMed Scopus Google Scholar). The also has an for DNA H. M. E. Y. K. Mutat. Res. 1994; PubMed Scopus Google Scholar), and repair of oxidative DNA in cell extracts has been by several this M. Nucleic Acids Res. 1998; PubMed Scopus Google Scholar, M.S. Lindahl T. Proc. Natl. Acad. Sci. U. S. A. 1993; 90: PubMed Scopus Google Scholar). no role for the in BER has been is that the is involved in the of 8-oxoguanine in DNA and BER proteins in processing of this There is from studies in mammalian cell extracts that DNA polymerase β is the major polymerase in single nucleotide gap BER R.W. R. H. Singhal R.K. R. K. Wilson S.H. Nature. 1996; PubMed Scopus Google Scholar, G. A. Lindahl T. Mol. Cell. Biol. 1992; PubMed Scopus Google Scholar, K. M.K. Nucleic Acids Res. 1996; PubMed Scopus Google Scholar, R.K. R. Wilson S.H. J. Biol. Chem. 1995; 270: Full Text Full Text PDF PubMed Scopus Google Scholar). DNA polymerase β has an intrinsic activity that the 5′ sugar phosphate by β elimination Y. Kim K. 1995; PubMed Scopus Google Scholar, R. Wilson S.H. J. Biol. Chem. 1996; 271: Full Text Full Text PDF PubMed Scopus Google Scholar). this a role in the single nucleotide patch repair pathway, it both the 5′ sugar phosphate generated by DNA glycosylase and AP endonuclease and also fills in the 1-nucleotide gap. In the polβ-deficient cell extracts the repair of uracil and AP sites is accomplished by a PCNA-dependent mechanism and results in a 2–5-nucleotide-long repair patch (16Biade S. Sobol R.W. Wilson S.H. Matsumoto Y. J. Biol. Chem. 1998; 273: 898-902Abstract Full Text Full Text PDF PubMed Scopus (179) Google Scholar, 17Fortini P. Pascucci B. Parlanti E. Sobol R.W. Wilson S.H. Dogliotti E. Biochemistry. 1998; 37: 3575-3580Crossref PubMed Scopus (200) Google that removal of 8-oxoguanine in polβ-deficient cell extracts was only accomplished through a long patch repair and one of the repair events involves a single nucleotide repair patch mechanism incorporation the incorporation by long patch long patch repair, flap endonuclease activity the 5′ sugar phosphate residue as a part of a and is not to generate a one nucleotide gap M.S. B. Park M.S. R.A. S. J. Biol. Chem. 1996; Full Text Full Text PDF Scopus Google Scholar, K. S. Matsumoto Y. J. Biol. Chem. 1998; 273: Full Text Full Text PDF PubMed Scopus Google Scholar). that in addition to long patch repair, mechanism is involved in the repair of 8-oxoguanine in polβ-deficient cell extracts. human can a β elimination reaction (9Radicella J.P. Dherin C. Desmaze C. Fox M.S. Boiteux S. Proc. Natl. Acad. Sci. U. S. A. 1997; 94: 8010-8015Crossref PubMed Scopus (571) Google Scholar, 10Roldan-Arjona T. Wei Y.F. Carter K.C. Klungland A. Anselmino C. Wang R.P. Augustus M. Lindahl T. Proc. Natl. Acad. Sci. U. S. A. 1997; 94: 8016-8020Crossref PubMed Scopus (342) Google Scholar, 11Rosenquist T.A. Zharkov D.O. Grollman A.P. Proc. Natl. Acad. Sci. U. S. A. 1997; 94: 7429-7434Crossref PubMed Scopus (459) Google Scholar) and most probably can also removal of a 3′ sugar phosphate from an AP site M. A. M.R. Y. Nucleic Acids Res. 1997; PubMed Scopus Google Scholar). This that or in with can generate a 1-nucleotide gap in the of polβ, and it is that a polymerase can the 1-nucleotide gap. Fortini P. Pascucci B. Parlanti E. Sobol R.W. Wilson S.H. Dogliotti E. Biochemistry. 1998; 37: 3575-3580Crossref PubMed Scopus (200) Google Scholar) recently that a polβ-independent single nucleotide repair patch mechanism can in the repair of uracil in DNA in mammalian cell extracts. In Fortini P. Pascucci B. Parlanti E. Sobol R.W. Wilson S.H. Dogliotti E. Biochemistry. 1998; 37: 3575-3580Crossref PubMed Scopus (200) Google Scholar) studied the repair of a DNA containing a single uracil residue at a defined that repair in polβ-deficient cell extracts may be accomplished through a single nucleotide patch The polβ-independent single nucleotide patch repair pathway for removal of uracil and the one that in this for may different enzymes are In the used by Fortini P. Pascucci B. Parlanti E. Sobol R.W. Wilson S.H. Dogliotti E. Biochemistry. 1998; 37: 3575-3580Crossref PubMed Scopus (200) Google Scholar), uracil-DNA glycosylase the uracil from DNA and an AP In to hOGG1, uracil-DNA glycosylase not have intrinsic AP lyase activity, and the AP site is processed by AP endonuclease, which a nick with a 5′ sugar In the of the AP lyase activity of polβ, the single nucleotide patch repair observed by Fortini P. Pascucci B. Parlanti E. Sobol R.W. Wilson S.H. Dogliotti E. Biochemistry. 1998; 37: 3575-3580Crossref PubMed Scopus (200) Google Scholar) may be by β or by the β elimination of the 5′ sugar phosphate in the cell In the of 8-oxoguanine repair, observed involvement of a single nucleotide patch pathway. was for up to 50% of repair events in a polβ-deficient cell extracts. These data that AP lyase activity of is involved repair of 8-oxoguanine. Based on that this polβ-independent single nucleotide repair patch pathway 8-oxoguanine-DNA DNA polymerase or and DNA ligase as a There is a possibility that activity is involved in the removal of the 3′ sugar phosphate in the nick generated by also that proteins that are only in a mouse are involved in this pathway. is not in cell extracts from normal cells this mechanism with the single nucleotide patch repair pathway, but at it is involved as a pathway for repair of 8-oxoguanine in a polβ-deficient cell extracts. S. H. Wilson for the of the cell R. M. R. and S. are for of the