Human Nucleotide Excision Repair Efficiently Removes Chromium-DNA Phosphate Adducts and Protects Cells against Chromate Toxicity

Abstract

Intracellular reduction of carcinogenic Cr(VI) leads to the extensive formation of Cr(III)-DNA phosphate adducts. Repair mechanisms for chromium and other DNA phosphate-based adducts are currently unknown in human cells. We found that nucleotide excision repair (NER)-proficient human cells rapidly removed chromium-DNA adducts, with an average t½ of 7.1 h, whereas NER-deficient XP-A, XP-C, and XP-F cells were severely compromised in their ability to repair chromium-DNA lesions. Activation of NER in Cr(VI)-treated human fibroblasts or lung epithelial H460 cells was manifested by XPC-dependent binding of the XPA protein to the nuclear matrix, which was also observed in UV light-treated (but not oxidant-stressed) cells. Intracellular replication of chromium-modified plasmids demonstrated increased mutagenicity of binary Cr(III)-DNA and ternary cysteine-Cr(III)-DNA adducts in cells with inactive NER. NER deficiency created by the loss of XPA in fibroblasts or by knockdown of this protein by stable expression of small interfering RNA in H460 cells increased apoptosis and clonogenic death by Cr(VI), providing genetic evidence for the role of monofunctional chromium-DNA adducts in the toxic effects of this metal. The rate of NER of chromium-DNA adducts under saturating conditions was calculated to be ∼50,000 lesions/min/cell. Because chromium-DNA adducts cause only small changes in the DNA helix, rapid repair of these modifications in human cells indicates that the presence of major structural distortions in DNA is not required for the efficient detection of the damaged sites by NER proteins in vivo. Intracellular reduction of carcinogenic Cr(VI) leads to the extensive formation of Cr(III)-DNA phosphate adducts. Repair mechanisms for chromium and other DNA phosphate-based adducts are currently unknown in human cells. We found that nucleotide excision repair (NER)-proficient human cells rapidly removed chromium-DNA adducts, with an average t½ of 7.1 h, whereas NER-deficient XP-A, XP-C, and XP-F cells were severely compromised in their ability to repair chromium-DNA lesions. Activation of NER in Cr(VI)-treated human fibroblasts or lung epithelial H460 cells was manifested by XPC-dependent binding of the XPA protein to the nuclear matrix, which was also observed in UV light-treated (but not oxidant-stressed) cells. Intracellular replication of chromium-modified plasmids demonstrated increased mutagenicity of binary Cr(III)-DNA and ternary cysteine-Cr(III)-DNA adducts in cells with inactive NER. NER deficiency created by the loss of XPA in fibroblasts or by knockdown of this protein by stable expression of small interfering RNA in H460 cells increased apoptosis and clonogenic death by Cr(VI), providing genetic evidence for the role of monofunctional chromium-DNA adducts in the toxic effects of this metal. The rate of NER of chromium-DNA adducts under saturating conditions was calculated to be ∼50,000 lesions/min/cell. Because chromium-DNA adducts cause only small changes in the DNA helix, rapid repair of these modifications in human cells indicates that the presence of major structural distortions in DNA is not required for the efficient detection of the damaged sites by NER proteins in vivo. Nucleotide excision repair (NER) 1The abbreviations used are: NER, nucleotide excision repair; CPDs, cyclobutane pyrimidine dimers; PBS, phosphate-buffered saline; siRNA, small interfering RNA. is the major DNA repair mechanism responsible for the removal of UV light-induced DNA lesions and bulky DNA adducts generated by many chemical mutagens (1Wood R.D. Mitchell M. Sgouros J. Lindahl T. Science. 2001; 291: 1284-1289Crossref PubMed Scopus (1106) Google Scholar, 2Hanawalt P.C. Oncogene. 2002; 21: 8949-8956Crossref PubMed Scopus (357) Google Scholar). Elimination of DNA damage by NER is a highly coordinated process consisting of recognition of the damaged site, excision of a short oligonucleotide containing the DNA lesion, and filling in of the repair-generated gap by a DNA polymerase, followed by ligation of the nick. In vitro reconstitution experiments with protein preparations from human cells have identified six core factors that are required for recognition and excision of bulky DNA modifications: XPA protein, XPC HR23B complex, replication protein A heterotrimer, multisubunit transcription factor IIH complex, and two structure-specific nucleases, XPG and XPF-ERCC1 (3Araujo S.J. Tirode F. Coin F. Pospiech H. Syvaoja J.E. Stucki M. Hubscher U. Egly J.M. Wood R.D. Genes Dev. 2000; 14: 349-359Crossref PubMed Google Scholar). NER consists of two subpathways that specialize in the removal of DNA lesions from either the entire genome (global NER) or the transcribed strands (transcription-coupled NER) (2Hanawalt P.C. Oncogene. 2002; 21: 8949-8956Crossref PubMed Scopus (357) Google Scholar). The difference in these two subpathways lies in the mechanisms of lesion detection. The initial damage recognition in global NER is usually performed by the XPC-HR23B complex (4Sugasawa K. Ng J.M. Masutani C. Iwai S. van der Spek P.J. Eker A.P. Hanaoka F. Bootsma D. Hoeijmakers J.H. Mol. Cell. 1998; 2: 223-232Abstract Full Text Full Text PDF PubMed Scopus (742) Google Scholar, 5You J.S. Wang M. Lee S.H. J. Biol. Chem. 2003; 278: 7476-7485Abstract Full Text Full Text PDF PubMed Scopus (87) Google Scholar), which may require additional factors for sensing DNA modifications that cause relatively minor duplex distortions. For example, efficient global repair of cyclobutane pyrimidine dimers (CPDs) and recruitment of XPC are dependent on the presence of the UV-DDB (UV-damaged DNA-binding factor) protein complex (6Tang J.Y. Hwang B.J. Ford J.M. Hanawalt P.C. Chu G. Mol. Cell. 2000; 5: 737-744Abstract Full Text Full Text PDF PubMed Scopus (279) Google Scholar, 7Fitch M.E. Nakajima S. Yasui A. Ford J.M. J. Biol. Chem. 2003; 278: 46906-46910Abstract Full Text Full Text PDF PubMed Scopus (204) Google Scholar). In transcription-coupled NER, DNA lesions are detected by stalling of RNA polymerase II, followed by the recruitment of the NER core machinery with the help of three additional proteins, CSA, CSB, and XAB2 (2Hanawalt P.C. Oncogene. 2002; 21: 8949-8956Crossref PubMed Scopus (357) Google Scholar, 8Nakatsu Y. Asahina H. Citterio E. Rademakers S. Vermeulen W. Kamiuchi S. Yeo J.-P. Khaw M.-C. Saijo M. Kodo N. Matsuda T. Hoeijmakers J.H.J. Tanaka K. J. Biol. Chem. 2000; 275: 34931-34937Abstract Full Text Full Text PDF PubMed Scopus (108) Google Scholar). The most common substrates for NER are bulky base lesions causing a major disruption of hydrogen bonding (2Hanawalt P.C. Oncogene. 2002; 21: 8949-8956Crossref PubMed Scopus (357) Google Scholar). Smaller chemical modifications of DNA bases formed by oxidative damage and alkylating agents are usually repaired by the base excision repair process (2Hanawalt P.C. Oncogene. 2002; 21: 8949-8956Crossref PubMed Scopus (357) Google Scholar, 9Friedberg E.C. Walker G.C. Siede W. DNA Repair and Mutagenesis. American Society for Microbiology, Washington, D. C.1995Google Scholar). Although major caretakers of DNA bases are now known, the nature of human repair processes involved in preserving the integrity of the DNA phosphate backbone is not well understood. The DNA phosphate group is a frequent site of adduct formation by chemical carcinogens and chemotherapeutic drugs (10Singer B. Environ. Health Perspect. 1985; 62: 41-48Crossref PubMed Scopus (80) Google Scholar, 11Maccubbin A.E. Caballes L. Riordan J.M. Huang D.H. Gurtoo H.L. Cancer Res. 1991; 51: 886-892PubMed Google Scholar, 12Zhitkovich A. Voitkun V. Costa M. Biochemistry. 1996; 35: 7275-7282Crossref PubMed Scopus (162) Google Scholar). Alkylation of DNA phosphates generates alkylphosphotriesters that, in Escherichia coli, are repaired via a non-NER process involving the Ada protein (13McCarthy T.V. Lindahl T. Nucleic Acids Res. 1985; 13: 2683-2698Crossref PubMed Scopus (112) Google Scholar). Ada homologs have not been found in human cells (1Wood R.D. Mitchell M. Sgouros J. Lindahl T. Science. 2001; 291: 1284-1289Crossref PubMed Scopus (1106) Google Scholar, 9Friedberg E.C. Walker G.C. Siede W. DNA Repair and Mutagenesis. American Society for Microbiology, Washington, D. C.1995Google Scholar), raising the question of whether DNA phosphate adducts could be substrates for NER, which has not yet been clearly addressed. Protein extracts from hamster cells have been found to excise only very small amounts of methylphosphotriester-containing oligonucleotides (14Branum M.E. Reardon J.T. Sancar A. J. Biol. Chem. 2001; 276: 25421-25426Abstract Full Text Full Text PDF PubMed Scopus (88) Google Scholar), but this result could have reflected the inefficiency of the in vitro NER. However, persistence of DNA alkylphosphotriesters in human fibroblasts was reported to be independent of the NER status (15Bodell W.J. Singer B. Thomas G.H. Cleaver J.E. Nucleic Acids Res. 1979; 6: 2819-2829Crossref PubMed Scopus (87) Google Scholar), although the employed analytical methodology was not very specific. In this work, we examined the role of cellular NER in the removal of DNA phosphate modifications by determining the intracellular persistence and biological activity of chromium-DNA adducts in human cells with normal and deficient NER. Various Cr(III)-DNA adducts are formed after intracellular uptake and reduction of Cr(VI), which is a recognized human carcinogen causing major environmental concerns and significant exposure in several dozens of occupations (16Zhitkovich A. Wilson S.H. Suk W.A. Biomarkers of Environmentally Associated Disease: Technologies, Concepts, and Perspectives. CRC Press LLC, New York2002: 267-285Google Scholar). The main forms of chromium-DNA adducts in mammalian cells are ternary complexes generated by cross-linking of cysteine and histidine to DNA via a phosphate-bound Cr(III) atom (17Zhitkovich A. Voitkun V. Costa M. Carcinogenesis. 1995; 16: 907-913Crossref PubMed Scopus (132) Google Scholar, 18Quievryn G. Messer J. Zhitkovich A. Biochemistry. 2002; 41: 3156-3167Crossref PubMed Scopus (97) Google Scholar). All chromium-DNA adducts have been determined to be mutagenic in human cells (19Voitkun V. Zhitkovich A. Costa M. Nucleic Acids Res. 1998; 26: 2024-2030Crossref PubMed Scopus (147) Google Scholar, 20Zhitkovich A. Song Y. Quievryn G. Voitkun V. Biochemistry. 2001; 40: 549-560Crossref PubMed Scopus (106) Google Scholar, 21Quievryn G. Peterson E. Messer J. Zhitkovich A. Biochemistry. 2003; 42: 1062-1070Crossref PubMed Scopus (153) Google Scholar). We found that NER was a principal repair mechanism for chromium-DNA adducts in human cells, which establishes NER as the most comprehensive DNA repair system capable of removing damage from both the backbone and base components of the DNA structure. Rapid repair of weakly distorting chromium-DNA phosphate adducts indicates that the presence of major structural deformations in the DNA helix is not always necessary for the efficient recognition of DNA modifications by human NER. Cells—Human primary IMR90 fibroblasts and SV40-immortalized XP-A (XPA–, GM04312C) and XP-F (XPF–, GM08437B), XPA-complemented XP-A (XPA+, GM15876A), and repair-proficient (WT/SV, GM00637H) human fibroblasts were obtained from the Coriell Repository. Human lung epithelial H460 cells were purchased from American Type Culture Collection. Measurements of Chromium Adducts in Cellular DNA—Cells were treated with 1–5 μm K2CrO4 for 3 h in Dulbecco's modified Eagle's medium, washed twice with phosphate-buffered saline with normal medium, and for the of chromium-DNA adducts of cellular DNA and of chromium by were performed as G. Messer J. Zhitkovich A. Biochemistry. 2002; 41: 3156-3167Crossref PubMed Scopus (97) Google Scholar). The detection was of The of chromium adducts was determined by the t½ is the determined from the of the of adducts loss of was calculated the initial of lesions and their for the loss of chromium G. Zhitkovich A. Carcinogenesis. 2000; 21: PubMed Google Scholar). The average of chromium-DNA adducts in three cells was used as the rate of All rate were for In Cellular and were on to G. Peterson E. Messer J. Zhitkovich A. Biochemistry. 2003; 42: 1062-1070Crossref PubMed Scopus (153) Google or treated with for h or with Cr(VI) for 3 h, and to the the cells were washed twice with and in a modified 3 and for was followed by in for DNA was with in for were washed with for and with in for and for h with containing was performed by of primary for XPA and A for h followed by of and and for h All were in containing and were with containing were with were a and by Cr(III)-DNA adducts were generated by the with μm G. Messer J. Zhitkovich A. Biochemistry. 2002; 41: 3156-3167Crossref PubMed Scopus (97) Google Scholar). ternary cysteine-Cr(III)-DNA adducts, DNA was modified in the presence of μm Cr(VI) and cysteine A. Song Y. Quievryn G. Voitkun V. Biochemistry. 2001; 40: 549-560Crossref PubMed Scopus (106) Google Scholar). experiments were performed as A. Song Y. Quievryn G. Voitkun V. Biochemistry. 2001; 40: 549-560Crossref PubMed Scopus (106) Google Scholar, 21Quievryn G. Peterson E. Messer J. Zhitkovich A. Biochemistry. 2003; 42: 1062-1070Crossref PubMed Scopus (153) Google Scholar). In and chromium-modified plasmids were XP-A and fibroblasts and for of the plasmids was and the E. and the of and was on and of clonogenic cells were and treated with Cr(VI) or for 3 h or with for h, and were after was determined by A polymerase was detected by polymerase and protein extracts were obtained by of cells in containing and A and A were detected in obtained by of cells in of XPA in H460 of XPA expression in lung epithelial H460 cells was by with a a small interfering RNA was by of with and followed by ligation with a The to XPA are in were in cells by with plasmids protein and protein and H460 cells were twice and in the presence of for The of XPA was determined by of protein extracts obtained as for polymerase Repair of Adducts in and Human role of NER in the removal of chromium-DNA adducts was examined by determining the rate of repair of chromium adducts from DNA in cells and deficient in of the NER adducts were formed by of SV40-immortalized human fibroblasts with μm Cr(VI) for 3 h, a that not or changes a as determined by for and cells, and The DNA were 3 h after the to that both Cr(VI) and Cr(III)-DNA binding were that the loss of chromium-DNA adducts from cells was to XP-A cells and that followed the h XP-A cells chromium-DNA adducts the XP-A cells in the of chromium the h, whereas cells of the chromium adducts this The initial of chromium-DNA adducts in cells were and were to in cells the XPA and chromium DNA the of NER in the removal of chromium-DNA we the rate of repair of chromium adducts in fibroblasts and two that are deficient in other NER proteins, XPC and and and XP-F fibroblasts also a very removal of chromium-DNA adducts, which was with XP-A cells. The average of chromium-DNA adducts in three cells was h h in two cells NER of chromium-DNA damage not to be by as primary IMR90 fibroblasts a rate of with t½ h The loss of chromium in cells was by with intracellular phosphate A. Song Y. Quievryn G. Voitkun V. Biochemistry. 2001; 40: 549-560Crossref PubMed Scopus (106) Google Scholar). of the XPA Protein in UV and Cr(VI)-treated UV of cellular have found that the XPA protein the sites of DNA damage M. van A. W. Vermeulen W. Hoeijmakers J.H. van van Mol. Cell. 2001; Full Text Full Text PDF PubMed Scopus Google Scholar, S. M. D. van Hoeijmakers J.H. Vermeulen W. Mol. Cell. Biol. 2003; PubMed Scopus Google Scholar). In the of DNA the of XPA rapidly the the of with nuclear Because NER is the only of stable binding of this protein to nuclear DNA could be used as the of DNA lesions by NER in vivo. UV DNA damage by chemical agents could not be to a nuclear which a for the detection of We that the presence of complexes could by XPA with We binding of XPA to nuclear a which nuclear and a well nuclear D. S. J. Biol. PubMed Scopus Google Scholar). and were by this in we examined the nuclear of the XPA protein in UV light-treated cells UV light-treated (but not cells a nuclear of after the in of DNA with by the of to that in that the of XPA protein was to the nuclear of UV cells. of XPA protein the sites of UV DNA was found to be XPC-dependent S. M. D. van Hoeijmakers J.H. Vermeulen W. Mol. Cell. Biol. 2003; PubMed Scopus Google Scholar). we found that the stable of XPA with and the nuclear of UV light-treated cells required the presence of XPC protein these experiments that in was capable of the presence of damaged of fibroblasts also a nuclear of the XPA protein and recruitment to the nuclear experiments in binding of to of Cr(VI)-treated cells not that nuclear binding of the XPA protein was after h and was after h not which cells removed of the chromium-DNA adducts cells, of fibroblasts with μm Cr(VI) not cause in XPA binding to the nuclear 3 h result was not by the formation of chromium-DNA damage in cells, as and fibroblasts very initial of chromium-DNA adducts and chromium DNA XPA with of cells was also and to of Cr(VI) not an of XPC protein for the of NER complexes whether oxidative DNA damage also nuclear binding of we cells treated with a toxic of clonogenic was in stable XPA complexes in these cells, that of XPA in the nuclear of cells treated with toxic of Cr(VI) was not a result of of oxidative DNA lesions. nuclear binding of XPA was also in cells to of and not of in and role of NER in repair of chromium-DNA adducts was examined by chromium-modified plasmids in and of plasmids in cells on average a three of the to cells XPA deficiency only the of of that the major lesions are not substrates for NER. of Cr(III) with DNA generates monofunctional Cr(III)-DNA adducts, a of which to DNA Carcinogenesis. C. PubMed Scopus (108) Google Scholar). DNA are lesions Carcinogenesis. C. PubMed Scopus (108) Google Scholar, T. G.H. Biochemistry. 2002; 41: PubMed Scopus Google and repaired by processes P.J. Mol. Cell. Biol. 2000; PubMed Scopus Google Scholar, Res. 2001; PubMed Scopus Google Scholar). of mammalian cells to Cr(VI) generates ternary chromium-DNA adducts, which the cysteine-Cr(III)-DNA is the most frequent DNA (17Zhitkovich A. Voitkun V. Costa M. Carcinogenesis. 1995; 16: 907-913Crossref PubMed Scopus (132) Google Scholar, 18Quievryn G. Messer J. Zhitkovich A. Biochemistry. 2002; 41: 3156-3167Crossref PubMed Scopus (97) Google Scholar). of cysteine plasmids in cells increased both mutagenic and to cells and the of NER in repair of this major DNA of NER on of the biological of chromium-DNA adducts and NER in Cr(VI) we in and fibroblasts cells a and of polymerase and A Cr(VI) of polymerase and A of and A. M. J. Oncogene. 2003; PubMed Scopus Google Scholar). apoptosis in cells also to their after chromium-DNA damage The difference in clonogenic and cells for Cr(VI) was to that for is to be in NER-deficient cells to their to repair major adducts J.S. Wang M. Lee S.H. J. Biol. Chem. 2003; 278: 7476-7485Abstract Full Text Full Text PDF PubMed Scopus (87) Google Scholar, D. M. J.T. Sancar A. Mol. Cell. Biol. PubMed Scopus Google Scholar). We found significant of XPA status on clonogenic after with and for and that of Cr(VI)-treated fibroblasts was by the deficient repair of chromium-DNA adducts. Because the lung is the main of toxic and carcinogenic effects of Cr(VI), we also examined the role of NER in to chromium-DNA damage in human lung epithelial H460 cells. with exposure of H460 cells to Cr(VI) binding of XPA to the nuclear which after of DNA by The of NER and chromium-DNA adducts in of these cells was by XPA stable expression of The cells a in the XPA to the or cells, and this their NER by the of chromium-DNA adducts by from 7.1 to h of XPA by not the initial of chromium-DNA modifications μm and chromium DNA phosphates for XPA knockdown and cells, and μm and chromium DNA The difference in and H460 cells was that observed and which could be to the activity of NER in H460 cells. and H460 cells clonogenic after exposure to and a role of NER Cr(VI) is common to cells of and the of this repair process in the removal of chromium-DNA of chromium-DNA adducts in normal and fibroblasts from three clearly that NER status is the main determining factor in the intracellular persistence of these lesions. mutagenicity of two chromium-DNA adducts in cells and a of chromium-DNA modifications in lung epithelial H460 cells with expression of the XPA protein the of human NER in the removal of chromium-DNA Human NER was efficient in the detection and removal of chromium-DNA adducts, as by a short of these 7.1 h for human For which are to be the NER have a of h in mammalian cells D. M. E. E. J. Biol. Chem. 2000; 275: Full Text Full Text PDF PubMed Google Scholar, A. J. van J. 1995; 14: PubMed Scopus Google Scholar). CPDs, major UV light-induced DNA lesion, are removed by NER a with t½ h A. J. van J. 1995; 14: PubMed Scopus Google Scholar). The rate of NER of bulky adducts was found to be dependent on the of the initial with the from to h for a and of adducts, S. M. Carcinogenesis. 1995; 16: PubMed Scopus Google Scholar). on the with other chromium-DNA adducts to be a for cellular NER. of to repair is the rate of lesion removal of the reported repair and the initial of damage S. M. Carcinogenesis. 1995; 16: PubMed Scopus Google Scholar), we calculated that the rate of NER of adducts was The of that formed D. M. E. E. J. Biol. Chem. 2000; 275: Full Text Full Text PDF PubMed Google Scholar, A. J. van J. 1995; 14: PubMed Scopus Google were removed a rate of for chromium-DNA adducts rapid NER of and chromium for SV40-immortalized and primary IMR90 repair rate reflected of a very of adducts formed in the cells chromium DNA The calculated of repair are that a human on the of of core NER factor S.J. Wood R.D. Mol. Cell. Biol. 2001; 21: PubMed Scopus Google Scholar). not that chromium-DNA adducts are recognized and removed by NER The most forms of light-induced DNA damage are repaired (2Hanawalt P.C. Oncogene. 2002; 21: 8949-8956Crossref PubMed Scopus (357) Google Scholar, D. M. E. E. J. Biol. Chem. 2000; 275: Full Text Full Text PDF PubMed Google Scholar, A. J. van J. 1995; 14: PubMed Scopus Google Scholar), which many NER factors and the of repair complexes for the removal of The NER has been as a DNA lesion formed by chemical of the DNA that a significant disruption of base U. M. B. H. U. S. A. PubMed Scopus Google Scholar, K. T. Y. Masutani C. Iwai S. Hanaoka F. Genes Dev. 2001; PubMed Scopus Google Scholar). DNA duplex is not to the NER as DNA of are to repair by NER. However, the presence of DNA duplex distortions in the of a DNA is required for NER are repaired by human NER only in with base U. M. B. H. U. S. A. PubMed Scopus Google Scholar). In the of UV light-induced is a very the to NER and the of DNA by the a repaired a minor of whereas rapidly repaired DNA by D. 1995; 62: PubMed Scopus Google Scholar). of bulky DNA adducts has been to their of major distortions in the DNA structure. DNA phosphate adducts not major helix although the presence of structural changes is clearly a of phosphate adduct DNA by Nucleic Acids Res. 1998; 26: PubMed Scopus Google and the duplex by Chem. Res. 2003; 16: PubMed Scopus Google Scholar). of XP-A fibroblasts containing chromium DNA phosphates was only μm chromium providing biological evidence that adducts not major structural as were well by human cells. on a rapid repair of chromium-DNA phosphate adducts that the by could be a very of a NER lesion is a in NER and the presence of chemical modifications is to weakly distorting CPDs, removal by NER expression of the of the UV-DDB complex (2Hanawalt P.C. Oncogene. 2002; 21: 8949-8956Crossref PubMed Scopus (357) Google Scholar, J.Y. Hwang B.J. Ford J.M. Hanawalt P.C. Chu G. Mol. Cell. 2000; 5: 737-744Abstract Full Text Full Text PDF PubMed Scopus (279) Google Scholar), NER of chromium-DNA adducts not to be as SV40-immortalized cells with and primary IMR90 fibroblasts repaired chromium adducts with result is with the that weakly but bulky modifications be detected and by the core NER Cr(III) forms complexes in an (16Zhitkovich A. Wilson S.H. Suk W.A. Biomarkers of Environmentally Associated Disease: Technologies, Concepts, and Perspectives. CRC Press LLC, New York2002: 267-285Google Scholar), which bulky modifications that, be in either of the DNA on the of the for the chromium-DNA adducts are the or and this may for the of chromium lesions to adducts (14Branum M.E. Reardon J.T. Sancar A. J. Biol. Chem. 2001; 276: 25421-25426Abstract Full Text Full Text PDF PubMed Scopus (88) Google Scholar, W.J. Singer B. Thomas G.H. Cleaver J.E. Nucleic Acids Res. 1979; 6: 2819-2829Crossref PubMed Scopus (87) Google Scholar). of UV cells have detected nuclear of a of XPA after Chem. Res. 2003; 16: PubMed Scopus Google Scholar, M. M. M. J. PubMed Google Scholar). was not as evidence of nuclear binding of a of this nuclear which was as nuclear after and with The nuclear obtained by consists of a of core by nuclear whereas the employed a nuclear and a containing D. S. J. Biol. PubMed Scopus Google Scholar). that XPA complexes in global NER are to the of the nuclear matrix, whereas components of transcription-coupled as S. Saijo M. Citterio E. M. Hoeijmakers J.H. Tanaka K. U. S. A. 2002; PubMed Scopus Google Scholar), with the core