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PubMed1997

B lymphocytes of xeroderma pigmentosum or Cockayne syndrome patients with inherited defects in nucleotide excision repair are fully capable of somatic hypermutation of immunoglobulin genes.

Recent experiments have strongly suggested that the process of somatic mutation is linked to transcription initiation. It was postulated that a mutator factor loads onto the RNA polymerase and, during elongation, causes transcriptional arrest that activates DNA repair, thus occasionally causing errors in the DNA sequence. We report the analysis of the role of one of the known DNA repair systems, nucleotide excision repair (NER), in somatic mutation. Epstein-Barrvirus-transformed B cells from patients with defects in NER (XP-B, XP-D, XP-V, and CS-A) were studied. Their heavy and light chain genes show a high frequency of point mutations in the variable (V), but not in the constant (C) regions. This suggests that these B cells can undergo somatic hypermutation despite significant defects in NER. Thus, it is doubtful that NER is an essential part of the mechanism of somatic hypermutation of Ig genes. As an aside, NER seems also not involved in Ig gene switch recombination.

Adolescent↗

PubMed1988

DNA binding by [2,5-14C]N-nitrosopyrrolidine in excision-repair proficient and deficient strains of Salmonella. Evidence for a major premutagenic adduct.

Little is known about the nature and possible genotoxic effects of the DNA adducts formed by N-nitrosopyrrolidine (NPYR) in whole animals. DNA binding in DNA isolated from [2,5-14C]NPYR-treated Salmonella was studied and attempts were made to monitor DNA adducts and correlate DNA binding with mutagenesis. NPYR was metabolized by hamster liver S-9 fraction in the presence of S.typhimurium TA1535 (uvrB-) or TA1975(uvrB+). DNA isolated from TA1535 contained about three times as much radioactivity as that isolated from TA1975, and NPYR-induced mutagenesis was several-fold higher in TA1535. The fraction of radioactivity incorporated into TA1535 was approximately 10(-5). Thermal hydrolysis of the 14C-containing DNA at neutral pH, followed by precipitation, released approximately 2/3 of the radioactivity into the supernatant. HPLC analysis of the supernatant revealed one major peak. This peak was absent in DNA from TA1975. Acid hydrolysis of the DNA precipitate after neutral hydrolysis released most of the residual radioactivity. Several small peaks were observed after HPLC analysis of the TA1535 acid hydrolysate or the TA1975 acid hydrolysate. These results demonstrate that NPYR is capable of binding to Salmonella DNA yielding one major product after hydrolysis and this DNA binding product appears to be repaired by the excision repair system. The fact that the major peak of radioactivity released from Salmonella is only found in the strain which is efficiently reverted by NPYR suggests that mutagenesis is dependent on the DNA modification leading to this peak.

Animals↗

PubMed2001

Base excision repair processing of radiation-induced clustered DNA lesions.

Energy from low LET ionising radiation, such as X rays and gamma rays, is deposited in the water surrounding the DNA molecule such that between 2 to 5 radical pairs are generated within a radius of I to 4 nm. As a result, multiple single lesions, including oxidised purine or pyrimidine bases, sites of base loss, and single-strand breaks, can be formed in DNA from the same radiation energy deposition event. The single lesions in these so-called multiply damaged sites or clustered lesions are repaired by base excision repair. Here we show that clustered DNA damages are formed in bacterial cells by ionising radiation and are converted to lethal double-strand breaks during attempted repair. In wild type cells possessing the oxidative DNA glycosylases that recognise and cleave DNA at repairable single damages, double-strand breaks are formed at radiation-induced clusters during post-irradiation incubation and in a dose-dependent fashion. Mutant cells lacking these enzymes do not form double-strand breaks post-irradiation and are substantially more radioresistant than wild type cells. These radioresistant mutant cells can be made radiosensitive by overexpressing one of the oxidative DNA glycosylases. Thus the effect of the oxidative DNA glycosylases in potentiating DNA damage must be considered when estimating radiation risk.

Base Pair Mismatch↗

PubMed2006

[Clinical, biochemical and molecular characterization of rare genetic disorders, related to nucleotide excision repair (NER) system].

All living organisms are equipped with DNA repair systems that can cope with a wide variety of DNA lesions. Among these repair pathways, nucleotide excision repair (NER) is quite versatile, involved in the removal of a variety of bulky DNA lesions induced by ultraviolet light and chemical carcinogens and mutagens. The importance of NER for human health is illustrated mainly by the occurrence of rare life-threatening disorders such as Xeroderma Pigmentosum (XP), Cockayne Syndrome (CS) and Trichthiodystrophy (TTD). XP, CS and most TTD patients exhibit increased sensitivity to UV light and premature aging. XP is associated with a high incidence of skin tumors, CS is primarily a developmental disorder associated with failure to thrive, and psychomotor retardation. The authors report the clinical, biochemical and molecular aspects of the NER pathway in individuals suspected to have a DNA repair, NER type-related disease. These diseases are rare worldwide, but are frequent in Israel, probably due to the high rate of consanguinity among certain Arab, Druze and Jewish populations. Our laboratory is the only one in Israel, and one of very few labs world-wide that is performing DNA repair evaluation as a diagnostic test for DNA repair-deficient inherited diseases. Identification of the causative genes and proteins in suspected families will facilitate accurate diagnosis, genetic counseling, identification of couples at risk and prenatal diagnosis.

DNA↗

PubMed2004

Growth retardation, early death, and DNA repair defects in mice deficient for the nucleotide excision repair enzyme XPF.

Xeroderma pigmentosum (XP) is a human genetic disease which is caused by defects in nucleotide excision repair. Since this repair pathway is responsible for removing UV irradiation-induced damage to DNA, XP patients are hypersensitive to sunlight and are prone to develop skin cancer. Based on the underlying genetic defect, the disease can be divided into the seven complementation groups XPA through XPG. XPF, in association with ERCC1, constitutes a structure-specific endonuclease that makes an incision 5' to the photodamage. XPF-ERCC1 has also been implicated in both removal of interstrand DNA cross-links and homology-mediated recombination and in immunoglobulin class switch recombination (CSR). To study the function of XPF in vivo, we inactivated the XPF gene in mice. XPF-deficient mice showed a severe postnatal growth defect and died approximately 3 weeks after birth. Histological examination revealed that the liver of mutant animals contained abnormal cells with enlarged nuclei. Furthermore, embryonic fibroblasts defective in XPF are hypersensitive to UV irradiation and mitomycin C treatment. No defect in CSR was detected, suggesting that the nuclease is dispensable for this recombination process. These phenotypes are identical to those exhibited by the ERCC1-deficient mice, consistent with the functional association of the two proteins. The complex phenotype suggests that XPF-ERCC1 is involved in multiple DNA repair processes.

Animals↗

PubMed2001

Evidence in Escherichia coli that N3-methyladenine lesions induced by a minor groove binding methyl sulfonate ester can be processed by both base and nucleotide excision repair.

It has been previously reported that a neutral DNA equilibrium binding agent based on an N-methylpyrrolecarboxamide dipeptide (lex) and modified with an O-methyl sulfonate ester functionality (MeOSO(2)-lex) selectively affords N3-methyladenine lesions. To study the interaction of the neutral lex dipeptide with calf thymus DNA, we have prepared stable, nonmethylating sulfone analogues of MeOSO(2)-lex that are neutral and cationic. Thermodynamic studies show that both the neutral and monocationic sulfone compounds bind to DNA with K(b)'s of 10(5) in primarily entropy-driven reactions. To determine how the cytotoxic N3-methyladenine adduct generated from MeOSO(2)-lex is repaired in E. coli, MeOSO(2)-lex was tested for toxicity in wild-type E. coli and in mutant strains defective in base excision repair (tag and/or alkA glycosylases or apn endonuclease), nucleotide excision repair (uvrA), and both base and nucleotide excision repair (tag/alkA/uvrA). The results clearly demonstrate the cellular toxicity of the N3-methyladenine lesion, and the protective role of base excision glycosylase proteins. A novel finding is that in the absence of functional base excision glycosylases, nucleotide excision repair can also protect cells from this cytotoxic minor groove lesion. Interaction between base and nucleotide excision repair systems is also seen in the protection of cells treated with cis-diamminedichloroplatinum(II) but not with anti-(+/-)-r-7,t-8-dihydroxy-t-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene.

7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide↗

PubMedDate not supplied

Consequences of the depletion of cellular deoxynucleoside triphosphate pools on the excision-repair process in cultured human fibroblasts.

DNA excision repair requires the insertion of bases into gaps in the DNA which arise during the removal of damaged sites from the chromatin. The number of bases required is dependent on the amount of damage and the patch size of repair in response to the particular type of damage. In cells in which the ability to synthesize deoxynucleoside triphosphates (dNTPs) has been compromised, repair cannot proceed to completion following doses of DNA-damaging agents which induce repair that requires greater than the steady-state level of dNTPs. Repair is thus not equally sensitive to depletion of dNTPs when measured in rapidly cycling cells with relatively high dNTP pools or in non-cycling cells with significantly smaller pools. Critical depletion of dNTPs results in the production of long-lived DNA strand breaks at repairing sites and reduction in the number of sites initiating repair. On the other hand, elevation of dNTP pools to 10-50-fold normal levels did not inhibit repair. This indicates that dNTP pool depletion but not general pool-imbalance affects DNA excision repair.

Cells, Cultured↗

PubMed2001

Analysis of nucleotide excision repair by detection of single-stranded DNA transients.

Nucleotide excision repair (NER) removes bulky DNA lesions and is thus crucial for the protection against environmental carcinogens and UV light exposure. Deficiencies in NER cause increased mutation rates and chromosomal aberrations. Current methods for studying NER are mostly based on either quantitation of lesion removal or detection of repair DNA synthesis. Both have their limitations: lesion removal is inaccurate at very short times post-lesion, where the fraction of removal is low. Repair synthesis is difficult to apply to normally cycling cells due to the need to discriminate repair from replicative DNA synthesis. To overcome these problems we developed a method for analysis of NER based on detection of transient single-stranded (ss) DNA stretches generated at the nucleotide excision step. Cells are metabolically labelled with BrdU, exposed to UV-irradiation and the ssDNA transients generated during excision repair are detected using an anti-BrdU antibody. The method allows single-cell microscopic analysis of the distribution of DNA repair sites as well as kinetic analysis of the DNA repair response. Studies using various DNA repair-deficient cell lines indicate that the detection method integrates a number of pre-synthesis nucleotide excision repair stages. Thus, assembled repair sites can be detected even when they may not lead to complete resolution of the DNA lesion. Using this approach, we show that repair helicase-deficient cells differ from endonuclease-deficient cells.

Animals↗

PubMed2002

Repair of clustered DNA lesions. Sequence-specific inhibition of long-patch base excision repair be 8-oxoguanine.

Ionizing radiation induces clustered DNA damage where two or more lesions are located proximal to each other on the same or opposite DNA strands. It has been suggested that individual lesions within a cluster are removed sequentially and that the presence of a vicinal lesion(s) may affect the rate and fidelity of DNA repair. In this study, we addressed the question of how 8-oxoguanine located opposite to normal or reduced abasic sites would affect the repair of these sites by the base excision repair system. We have found that an 8-oxoguanine located opposite to an abasic site does not affect either the efficiency or fidelity of repair synthesis by DNA polymerase beta. In contrast, an 8-oxoguanine located one nucleotide 3'-downstream of the abasic site significantly reduces both strand displacement synthesis supported by DNA polymerase beta or delta and cleavage by flap endonuclease of the generated flap, thus inhibiting the long-patch base excision repair pathway.

DNA Damage↗

PubMed2004

Irofulven cytotoxicity depends on transcription-coupled nucleotide excision repair and is correlated with XPG expression in solid tumor cells.

BACKGROUND: Irofulven is a novel alkylating agent with promising clinical activity, particularly toward ovarian and hormone-refractory prostate cancers. To facilitate additional clinical development, we have aimed to identify biological markers associated with sensitivity to the compound. METHODS: Fibroblasts derived from patients with xeroderma pigmentosum or Cockayne's syndrome along with a panel of 20 human cancer cell lines (eight different tumor types) were examined to establish the importance of nucleotide excision repair proteins in the sensitivity to irofulven. RESULTS: Human cells deficient in nucleotide excision repair are up to 30-fold more sensitive to the cytotoxic effects of irofulven compared with repair-proficient controls, clearly indicating that nucleotide excision repair plays a crucial role in the sensitivity to the drug. Interestingly, our results show that irofulven-induced lesions are recognized by transcription-coupled repair but not by global genome repair. Another unique feature is the pronounced sensitivity of XPD and XPB helicase-deficient cells to the drug. Comparison of the IC50 values for irofulven, cisplatin, and ecteinascidin 743 with the expression levels of ERCC1, XPD, and XPG genes in different solid tumor cell lines shows no correlation between the expression levels of any of the three nucleotide excision repair proteins and the sensitivity to ecteinascidin 743. In contrast, expression of the XPG endonuclease was correlated with the cytotoxicity for irofulven and, to a lesser degree, for cisplatin. Importantly, XPG expression was also correlated with cellular nucleotide excision repair activity. CONCLUSIONS: Increasing evidence indicates that compromised nucleotide excision repair activity is frequent in several solid tumor types. The results presented here suggest that XPG expression in such tumors may be a useful marker to predict their sensitivity to irofulven.

Antineoplastic Agents, Alkylating↗

PubMed1986

Molecular approaches to the study of nucleotide excision repair in eukaryotes.

Very little is known about the molecular mechanism of nucleotide excision repair in eukaryotes. Studies on human cells have been stimulated by the availability of excision repair-defective cell lines from patients suffering from the autosomal recessive disease xeroderma pigmentosum (XP). Such studies have contributed significantly to an understanding of the genetic complexity of excision repair in human cells. However, to date, no human excision repair genes or gene products known to complement the repair defect in XP cells have been isolated. The yeast Saccharomyces cerevisiae is an interesting model for exploring the molecular mechanism of nucleotide excision repair in eukaryotic cells. As is true in human cells, multiple yeast genes are involved and at least five genes are required for the specific incision of UV-irradiated DNA in vivo. These five genes have been isolated by molecular cloning and the nucleotide sequences of four of them have been determined. Each of these cloned genes is being used for overexpression of protein.

Base Sequence↗

PubMed1992

Mutagenic DNA repair in Escherichia coli. XXI. A stable SOS-inducing signal persisting after excision repair of ultraviolet damage.

Mutations to streptomycin resistance induced by ultraviolet light in Escherichia coli can lose their susceptibility to photoreversing light during excision repair and in the absence of chromosomal replication and protein synthesis, i.e., under conditions where SOS induction cannot occur. Using fusions of lac with sulA and umuC we have shown that after excision of UV damage in the presence of chloramphenicol there is a persisting, relatively stable signal capable of inducing SOS genes when protein synthesis is subsequently permitted. The persisting signal is formed roughly in proportion to the square of the UV dose and is about 30% photoreversible. It is suggested that the persisting SOS-inducing signal comprises a UV photoproduct (the target lesion) opposite a gap in the opposing DNA strand, and is formed by excision of one (the ancillary lesion) of a pair of closely opposed photoproducts. Calculations suggest that as few as two or three such configurations in a cell can lead to induction of sulA when protein synthesis is permitted. It is not clear whether these configurations can directly induce the SOS system because of their region of single-stranded DNA or whether the ultimate SOS-inducing signal is a more extensive single-stranded region formed when such configurations encounter a replication fork. Photoproduct/gap configurations have been previously suggested to be potentially mutagenic. UV-induced mutations to streptomycin resistance are mostly at A:T sites and are not photoreversible in fully SOS-induced bacteria in the absence of excision repair, indicating that they are not targeted at cyclobutane-type pyrimidine dimers. In SOS-induced excision-proficient bacteria there is about 39% photoreversibility which is rapidly lost after UV. This photoreversibility is attributed to many ancillary lesions being cyclobutane-type pyrimidine dimers which are excised leading to the exposure of target lesions on the opposing strand which, at these particular sites, are mostly non-photoreversible photoproducts.

Bacterial Proteins↗

PubMed2004

[Expression of DNA excision repair enzymes and lung cancer prognosis].

OBJECTIVE: To study the expression levels of three DNA damage excision repair enzymes: excision repair cross-complementing rodent repair deficiency gene 2 (ERCC2), uracil DNA glycosylase (UDG), and proliferating cell nuclear antigen (PCNA), in different lung tissues and their relationship with lung cancer prognosis. METHODS: The expression levels of ERCC2, UDG, and PCNA protein were detected using immunohistochemistry method. Cancer tissues and normal tissues adjacent to the cancer from 61 cases of lung carcinoma, and tissue samples from 18 cases of benign lung disease were studied. The relationship among ERCC2, UDG, and PCNA expression levels with lung cancer development and prognosis were studied using Ridit analysis method. RESULTS: The expression levels of all three proteins were not significantly different between cancer tissues and a normal tissues adjacent to the cancer (P > 0.05); but significantly different between cancer tissues and benign tissues, and between normal tissues adjacent to the cancer and benign tissues (P < 0.05). ERCC2 and UDG levels were higher in benign tissues than those in cancer and cancer adjacent tissues, while the PCNA level was the opposite. Only the UDG level in cancer adjacent normal tissues showed no significant difference compared to that of benign tissues (P > 0.05). There were no relationship among age, smoke, cancer metastasis, cancer type and ERCC2, UDG, PCNA expression levels. ERCC2 also showed no relationship with degree of malignancy and cancer size, while UDG and PCNA expression levels were correlated with cancer malignancy and cancer size (P < 0.05). Low UDG and high PCNA expression levels were correlated with higher malignancy and larger tumors. CONCLUSION: The expression levels of ERCC2, UDG and PCNA were significantly different in benign lung tissues, lung cancer tissues and lung cancer adjacent normal tissues. ERCC2 showed no significant relationship with lung cancer prognosis, while patients with low UDG and high PCNA expressions were more likely to have higher malignancy and larger tumors. UDG and PCNA were possible markers for evaluating lung cancer prognosis.

Adult↗

PubMed2001

DNA synthesis and dRPase activities of polymerase beta are both essential for single-nucleotide patch base excision repair in mammalian cell extracts.

In mammalian cells the majority of altered bases in DNA are processed through a single-nucleotide patch base excision repair mechanism. Base excision repair is initiated by a DNA glycosylase that removes a damaged base and generates an abasic site (AP site). This AP site is further processed by an AP endonuclease activity that incises the phosphodiester bond adjacent to the AP site and generates a strand break containing 3'-OH and 5'-sugar phosphate ends. In mammalian cells, the 5'-sugar phosphate is removed by the AP lyase activity of DNA polymerase beta (Pol beta). The same enzyme also fills the gap, and the DNA ends are finally rejoined by DNA ligase. We measured repair of oligonucleotide substrates containing a single AP site in cell extracts prepared from normal and Pol beta-null mouse cells and show that the reduced repair in Pol beta-null extracts can be complemented by addition of purified Pol beta. Using this complementation assay, we demonstrate that mutated Pol beta without dRPase activity is able to stimulate long patch BER. Mutant Pol beta deficient in DNA synthesis, but with normal dRPase activity, does not stimulate repair in Pol beta-null cells. However, under conditions where we measure base excision repair accomplished exclusively through a single-nucleotide patch BER, neither dRPase nor DNA synthesis mutants of Pol beta alone, or the two together, were able to complement the repair defect. These data suggest that the dRPase and DNA synthesis activities of Pol beta are coupled and that both of these Pol beta functions are essential during short patch BER and cannot be efficiently substituted by other cellular enzymes.

Amino Acid Substitution↗

PubMed1976

Effect of excision repair on azide-induced mutagenesis.

Azide mutagenesis was investigated in Salmonella typhimurium and Escherichia coli. Azide was highly effective in inducing his+ revertants in excision-repair deficient (uvrB) derivatives of S. typhimurium hisG46 and in inducing high frequencies of 5-fluorouracil resistant mutants in excision-repair deficient (uvrA) derivatives of E. coli B/r WP2. In excision-repair plus strains, azide was only a marginal or ineffective mutagen, demonstrating that the bacterial excision-repair system could repair nearly all azide-induced damage. This observation suggests that the initial azide-induced lesion causes a major DNA helix distortion recognizable by the excision-repair endonucleases. The presence of recombination deficient (recB or recC) genes in combination with uvrA increased E. coli sensitivity to azide killing, but depressed azide mutagenicity. These results are similar to those reported for UV-induced mutagenesis with the E. coli strains and suggest that post-replication repair might be the error-prone step in the repair process. Azide mutagenesis specificity is, however, unique and different from UV, as demonstrated by inability of azide to revert the ochre try locus in E. coli WP2s. These results show that the initial azide-induced DNA damage is highly specific but different from UV-induced DNA damage. Metabolic inhibitors, similar in action to azide, did not induce mutations in S. typhimurium strain TA1530, a strain highly susceptible to azide mutagenesis, thus ruling out the possibility that azide mutagenesis was due to peroxide accumulation. A mechanism based on in vivo activation of azide to the actual mutagen is proposed.

Azides↗

PubMed1985

Stimulation of deoxyribonucleic acid excision repair in human fibroblasts pretreated with sodium butyrate.

The effect of pretreatment with sodium butyrate on DNA excision repair was studied in intact and permeable confluent (i.e., growth-inhibited) diploid human fibroblasts. Exposure to 20 mM sodium butyrate for 48 h increased subsequent ultraviolet (UV)-induced [methyl-3H]thymidine incorporation by intact AG1518 fibroblasts by 1.8-fold and by intact IMR-90 fibroblasts by 1.2-1.3-fold. UV-induced incorporation of deoxy[5-3H]cytidine, deoxy[6-3H]cytidine, and deoxy[6-3H]uridine, however, showed lesser degrees of either stimulation or inhibition in butyrate-pretreated cells. This result suggested that measurements of butyrate's effect on DNA repair synthesis in intact cells are confounded by simultaneous changes in nucleotide metabolism. The effect of butyrate on excision repair was also studied in permeable human fibroblasts in which excision repair is dependent on exogenous nucleotides. Butyrate pretreatment stimulated UV-induced repair synthesis by 1.3-1.7-fold in permeable AG1518 cells and by 1.5-2-fold in permeable IMR-90 cells. This stimulation of repair synthesis was not due to changes in repair patch size or composition or in the efficiency of DNA damage production but rather resulted from a butyrate-induced increase in the rate of damage-specific incision of DNA. The increased rate of incision in butyrate-pretreated cells could be due either to increased levels of enzymes mediating steps in excision repair at or before incision or to alterations in chromatin structure making damage sites in DNA more accessible to repair enzymes.

Adenosine Triphosphate↗

PubMed1994

UV induction of excision repair enzymes detected in protein extracts from Schizosaccharomyces pombe.

Induction of genes and proteins after DNA damaging treatment is well documented in various biological systems. In order to monitor repair activity in Schizosacchromyces pombe, we adapted the biochemical assay that allowed specific quantification of excision repair in mammalian cells (Wood et al. 1988, Cell, 53, 97-106) to yeast-free extracts. Repair synthesis determined on UV-damaged plasmid DNA with S. pombe total protein extract relied on base excision repair and not nucleotide excision repair. Under conditions that allowed optimal repair activity, an enhanced repair synthesis was found with extract from yeast previously irradiated with UV light (254 nm). A 4-fold induction factor was obtained with 70 J/m2 irradiation dose after 40 min incubation post-irradiation. This base excision repair activity on UV photoproducts was transiently induced since it returned to the level of untreated yeast after about 2 hours post-irradiation.

Cell-Free System↗

PubMed1989

Interactions between yeast photolyase and nucleotide excision repair proteins in Saccharomyces cerevisiae and Escherichia coli.

The PHR1 gene of Saccharomyces cerevisiae encodes a DNA photolyase that catalyzes the light-dependent repair of pyrimidine dimers. In the absence of photoreactivating light, this enzyme binds to pyrimidine dimers but is unable to repair them. We have assessed the effect of bound photolyase on the dark survival of yeast cells carrying mutations in genes that eliminate either nucleotide excision repair (RAD2) or mutagenic repair (RAD18). We found that a functional PHR1 gene enhanced dark survival in a rad18 background but failed to do so in a rad2 or rad2 rad18 background and therefore conclude that photolyase stimulates specifically nucleotide excision repair of dimers in S. cerevisiae. This effect is similar to the effect of Escherichia coli photolyase on excision repair in the bacterium. However, despite the functional and structural similarities between yeast photolyase and the E. coli enzyme and complementation of the photoreactivation deficiency of E. coli phr mutants by PHR1, yeast photolyase failed to enhance excision repair in the bacterium. Instead, Phr1 was found to be a potent inhibitor of dark repair in recA strains but had no effect in uvrA strains. The results of in vitro experiments indicate that inhibition of nucleotide excision repair results from competition between yeast photolyase and ABC excision nuclease for binding at pyrimidine dimers. In addition, the A and B subunits of the excision nuclease, when allowed to bind to dimers before photolyase, suppressed photoreactivation by Phr1. We propose that enhancement of nucleotide excision repair by photolyases is a general phenomenon and that photolyase should be considered an accessory protein in this pathway.

Binding, Competitive↗