Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:6.5.1.2 (DNA ligase)
2,749 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Rejoining of DNA single-strand breaks generated by treatment of plasmids with gamma-rays, neocarzinostatin, or bleomycin was catalyzed inefficiently by human cell extracts. The reaction was strongly promoted by the addition of NAD+, which was employed for rapid and transient synthesis of poly(ADP-ribose). The DNA rejoining reaction was accompanied by DNA repair replication, apparently due to replacement of damaged residues at termini. Selective depletion of poly(ADP-ribose) polymerase from cell extracts improved the repair of DNA exposed to a variety of DNA-damaging agents by removing the NAD+ dependence of the repair reaction. NAD(+)-promoted DNA repair by soluble cell extracts also occurred with alkylated DNA as substrate and was suppressed by 3-aminobenzamide. A similar stimulatory effect by NAD+ was observed for repair of ultraviolet-irradiated DNA, and this could be ascribed to the presence of pyrimidine hydrates as minor radiation-induced DNA lesions. No effect was observed on the sealing of gamma-irradiated DNA by supplementation of cell extracts with purified mammalian DNA ligase I or DNA ligase II. The results indicate that poly(ADP-ribose) polymerase interferes with base excision-repair processes because bound enzyme molecules block DNA strand interruptions. Release of bound poly-(ADP-ribose) polymerase following automodification, or physical removal of the protein from reaction mixtures, facilitates DNA repair.
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PMID:NAD(+)-dependent repair of damaged DNA by human cell extracts. 768 Jun 46

To test the influence of pyrimidine methyl groups on DNA flexibility and helix repeat, two sets of 14 mixed sequence DNA molecules, spanning a range of lengths from 158 to 180 base pairs, were cyclized with T4 DNA ligase. The two sets differed only in that the Cyt-5 positions of all cytosines (80-90 cytosine residues per molecule) were fully methylated in the members of one set. Determination of the molar cyclization factors, persistence lengths, helix repeats, and torsional elastic constants revealed no significant differences between the two sets. These results imply that, at least for mixed sequence DNA, the biological consequences of cytosine methylation are likely to derive from either local structural distortions in the helix, which do not propagate as altered twist, or from direct protein-methyl cytosine interactions.
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PMID:Investigation of the influence of cytosine methylation on DNA flexibility. 781 73

Tanning is a protective response of ultraviolet (UV)-irradiated skin that decreases damage from subsequent sun exposures by increasing the epidermal content of melanin, a brown-black pigment that absorbs light energy throughout the UV and visible portions of the electromagnetic spectrum. The melanin pigment is made by epidermal melanocytes and transferred to surrounding keratinocytes. The action spectrum, time course, and histologic features of tanning are well studied, but the initiating molecular events are unknown. Previous work has shown that T4 endonuclease V, a prokaryotic DNA repair enzyme that catalyzes the first and rate-limiting step in repair of UV-induced pyrimidine dimers, delivered in carrier liposomes (T4N5), enhances repair of UV-induced DNA damage in cultured human cells and protects against photocarcinogenesis in an animal model. We now report that T4N5 treatment enhances UV-induced melanogenesis, as measured by melanin content, tyrosinase activity, 14C-dopa incorporation, and visual assessment in both S91 murine melanoma cells and human melanocytes. T4N5 treatment also increases cell yields following UV irradiation. These data suggest that tanning can be stimulated through enhanced DNA repair.
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PMID:Treatment of human melanocytes and S91 melanoma cells with the DNA repair enzyme T4 endonuclease V enhances melanogenesis after ultraviolet irradiation. 822 26

Exposure of skin to ultraviolet (UV) radiation inhibits the induction of delayed-type hypersensitivity (DTH) responses initiated at a distant, unirradiated site. Recent studies attributed this form of immune suppression to DNA damage in the form of cyclobutane pyrimidine dimers (CPD). In the present study, we investigated the protective defects of sunscreens on UV-induced systemic suppression of DTH to Candida albicans, inflammation, and DNA damage. The photoprotective effects of sunscreen preparations containing 8% octyl-N-dimethyl-p-aminobenzoate, 7.5% 2-ethylhexyl-p-methoxycinnamate, or 6% benzophenone-3 were studied in C3H mice exposed to a single dose of 500 mJ/cm2 UVB radiation from FS40 sunlamps. Inflammation was determined by the amount of skin edema at the site of UV irradiation, and DNA damage was assessed by measuring the frequency of endonuclease-sensitive sites in the epidermis. Application of the sunscreens before UV irradiation gave 75-97% protection against UV-induced edema, 67-91% protection against formation of CPD, but only 30-54% protection against suppression of DTH. In contrast, the topical application of liposomes containing a CPD-specific DNA repair enzyme immediately after UV irradiation resulted in 82% protection against suppression of DTH, but at best, 39% protection against skin edema. These findings demonstrate that sunscreens give less protection against UV-induced immune suppression than against skin edema and CPD formation. Furthermore, they suggest that less DNA damage is required to cause UV-induced immune suppression than to cause sunburn.
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PMID:Effects of sunscreens and a DNA excision repair enzyme on ultraviolet radiation-induced inflammation, immune suppression, and cyclobutane pyrimidine dimer formation in mice. 840 17

Reductive methylation of the alpha NH2 moiety of the DNA repair enzyme T4 endonuclease V has been shown previously to eradicate both the N-glycosylase and apyrimidinic/apurinic lyase activities of the enzyme (Schrock, R. D., III, and Lloyd, R. S. (1991) J. Biol. Chem. 266, 17631-17639). The present study uses the technique of site-directed mutagenesis to investigate the important parameters involved in the cleavage mechanism. The prediction was that the addition of an amino acid in the immediate NH2-terminal region of the protein would alter the proximity of the alpha NH2 moiety of Thr2 to its target, thereby severely compromising the enzyme's catalytic activity. However, substitutions in this region generally should be tolerated. To test this hypothesis, three substitutions of the NH2-terminal amino acid were produced: Ser2 (T2S), Val2 (T2V), and Pro2 (T2P). An addition mutant was also produced by adding a glycine between the first and second amino acids of the protein (Thr2-Gly-Arg3) (+Gly). The T2P and +Gly mutants had negligible pyrimidine dimer-specific N-glycosylase activity as well as negligible pyrimidine dimer-specific nicking activity in vitro. Conversely, the T2S enzyme exhibited wild type levels of activity and the T2V exhibited intermediate levels of activity in vitro. Results from ultraviolet (UV) survival studies of the mutant enzymes indicated that the in vivo activities of these enzymes were directly correlated to the enzymes' ability to cleave at pyrimidine dimers in vitro. These results indicate that a critical parameter for the functionality of endonuclease V is the relative distance between the primary alpha NH2 group in the active site of the enzyme and those elements responsible for DNA binding and pyrimidine dimer recognition.
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PMID:Site-directed mutagenesis of the NH2 terminus of T4 endonuclease V. The position of the alpha NH2 moiety affects catalytic activity. 841 66

DNA photolyase is a light-dependent DNA repair enzyme. It binds to cyclobutane pyrimidine dimers <PyrPyr> in DNA and upon excitation with a blue light photon splits the cyclobutane ring and restores the pyrimidines to native forms. The enzyme is specific for pyrimidine dimers, and it is not known to catalyze any other reaction either in ground or in excited state. However, when photolyase binds to <PyrPyr> but cannot catalyze repair because of lack of photoreactivating light, it still aids DNA repair by stimulating the nucleotide excision repair system. Recently, it was found that yeast photolyase binds to other lesions in DNA. In particular, the binding to cisplatin damaged DNA was highly specific. However, in vivo experiments revealed that this binding, in contrast to <PyrPyr> binding, did not stimulate but actually inhibited the removal of cisplatin damage by excision repair and hence photolyase sensitized cells to killing by cisplatin. In the present study, it is demonstrated that Escherichia coli DNA photolyase binds specifically to cisplatin 1,2-d(GpG) intrastrand cross-link and stimulates the removal of the lesion by E. coli excision nuclease in vitro. In agreement with the in vitro data, in vivo experiments revealed that photolyase makes cells more resistant to cisplatin killing.
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PMID:The other function of DNA photolyase: stimulation of excision repair of chemical damage to DNA. 851 44

T4 endonuclease V is a DNA repair enzyme from bacteriophage T4 that catalyzes the first reaction step of the pyrimidine dimer-specific base excision repair pathway. The crystal structure of this enzyme complexed with a duplex DNA substrate, containing a thymine dimer, has been determined at 2.75 A resolution. The atomic structure of the complex reveals the unique conformation of the DNA duplex, which exhibits a sharp kink with a 60 degree inclination at the central thymine dimer. The adenine base complementary to the 5' side of the thymine dimer is completely flipped out of the DNA duplex and trapped in a cavity on the protein surface. These structural features allow an understanding of the catalytic mechanism and implicate a general mechanism of how other repair enzymes recognize damaged DNA duplexes.
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PMID:Atomic model of a pyrimidine dimer excision repair enzyme complexed with a DNA substrate: structural basis for damaged DNA recognition. 852 94

DNA repair processes and UV-filtering pigments protect organisms from the cytotoxicity of UV light and endow plants with a high degree of natural UV resistance. In an attempt to further enhance this UV resistance we have constructed transgenic tobacco lines that express a DNA repair enzyme encoded by the bacteriophage T4 denV gene. The denV gene encodes endonuclease V, an enzyme which initiates base excision repair of cyclobutane pyrimidine dimers. Its presence is expected to provide transgenotes with a repair pathway complementary to, but likely distinct from, the repair pathways found in tobacco. The denV gene, flanked by a CaMV 35S promoter and poly(A) addition site, was introduced into tobacco and mature plants regenerated. The transgenotes expressed high levels of a UV-specific endonuclease and no such activity was found in control plants. Curiously, assays which detected several different biological endpoints showed that the denV+ transgenotes were also hypersensitive to UV-C light. This hypersensitivity segregated with the denV gene and was not caused by altered concentrations of UV-filtering pigments. Moreover, the denV+ transgenotes were also hypersensitive to high levels of baseless lesions that would be generated by a transgenically expressed beta-eliminating lyase such as endonuclease V.
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PMID:Tobacco plants expressing T4 endonuclease V show enhanced sensitivity to ultraviolet light and DNA alkylating agents. 860 70

We purified a homologue of the Escherichia coli DNA repair enzyme endo nuclease III 5000-fold from calf thymus which, like endonuclease III, demonstrates DNA-glycosylase activity against pyrimidine hydrates and thymine glycol and AP lyase activity (DNA strand cleavage at AP sites via beta-elimination). The functional similarity between the enzymes suggested a strategy for definitive identification of the bovine protein based on the nature of its enzyme-substrate (ES) intermediate. Prokaryotic DNA glycosylase/AP lyases function through N-acylimine (Schiff's base) ES intermediates which, upon chemical reduction to stable secondary amines, irreversibly cross link the enzyme to oligodeoxynucleotides containing substrate modified bases. We incubated endonuclease III with a 32P- labeled thymine glycol-containing oligodeoxynucleotide in the presence of NaCNBH3. This resulted in an increase in the apparent molecular weight of the enzyme by SDS-PAGE. Phosphorimaging confirmed irreversible cross linking between enzyme and DNA. Identical treatment of the most purified bovine enzyme fraction resulted in irreversible cross linking of the oligodeoxynucleotide to a predominant 31 kDa species. Amino acid analysis of the 31 kDa species revealed homology to the predicted amino acid sequence of a Caenorhabditis elegans 27.8 kDa protein which, in turn, has homology to endonuclease III. The translated amino acid sequences of two partial 3' cDNAs, from Homo sapiens and Rattus sp., also demonstrate homology to the C. elegans and bovine sequences suggesting a homologous family of endonuclease III-like DNA repair enzymes is present throughout phylogeny.
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PMID:Purification of a mammalian homologue of Escherichia coli endonuclease III: identification of a bovine pyrimidine hydrate-thymine glycol DNAse/AP lyase by irreversible cross linking to a thymine glycol-containing oligoxynucleotide. 861 53

In Escherichia coli and related bacteria, the product of gene dcm methylates the second cytosine of 5'-CCWGG sequences (where W is A or T). Deamination of 5-methylcytosine (5meC) results in C to T mutations. The mutagenic potential of 5meC is reduced by a system called very short patch (VSP) repair, which replaces T with C. T:G and U:G mispairs in the methylatable sequence and in related sequences are recognized by the product of vsr, a gene adjacent to dcm. Vsr creates a nick just 5' of the mispaired pyrimidine to initiate the repair. Additional products known to be required for VSP repair are DNA polymerase I and DNA ligase. MutS and MutL have a stimulatory role but are not required. The ability of Vsr to recognize T:G mispairs in sequences related to CCWGG is probably responsible for over- and under-representation of certain tetranucleotides in the E. coli genome. Although VSP repair reduces spontaneous mutations at 5meCs in replicating bacteria, mutation hot-spots persist at these sites. Under conditions that more accurately mimic the natural environment of E. coli, VSP repair appears to be effective in preventing mutation at 5meC.
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PMID:Very short patch repair: reducing the cost of cytosine methylation. 873 26


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