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:3.1.30.2 (endonuclease)
18,621 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

DNA photosensitization by several furocoumarins (including 3-carbethoxypsoralen (3-CPs), 8-methoxypsoralen (8-MOP), 5-methoxypsoralen (5-MOP) and angelicin was investigated by using DNA sequencing methodology. 3-CPs induces photo-oxidation of guanine residues leading to alkali-labile sites in DNA (revealed by hot piperidine), whereas 8-MOP, 5-MOP and angelicin do not. There is a preferential photo-oxidation of G when located on the 5' side of GG doublets, likely to reflect a better accessibility of the G moiety in such a context. Mechanisms operating via both radicals (type I) and singlet oxygen (type II) are involved in the photo-oxidation of G residues by 3-CPs. Photo-oxidized G residues are produced independently of the formation of photoadducts, and scavengers of singlet oxygen or radicals do not inhibit photobinding of 3-CPs to DNA. This leads us to propose that covalent photoadducts arise from the intercalated excited sensitizer molecules, whereas G photo-oxidations are produced either by electron transfer reactions involving bound 3-CPs or by energy transfer to molecular oxygen, thereby producing singlet oxygen that subsequently reacts with guanine bases. Quantification of both types of DNA lesions indicated that in vitro photo-oxidized G residues are produced in DNA by 3-CPs plus ultraviolet light at least to the same extent as photoadducts, under our conditions. A calf thymus redoxyendonuclease, equivalent to the endonuclease III of Escherichia coli, specific for oxidative DNA damages, recognizes and cleaves DNA at sites of photo-oxidized G residues. The extent of the cleavage by this enzyme was close to that observed by hot piperidine and followed the amount of photo-oxidized G residues produced when the lifetime of excited oxygen species is modified. The redoxyendonuclease did not incise DNA treated with 8-MOP, 5-MOP or angelicin plus ultraviolet light. The exonuclease III and endonuclease IV of E. coli also involved in the repair of oxidative DNA damage, convert the replicative form I of 3-CPs-treated DNA to replicative form II. This suggests that the lesions recognized by these enzymes are apurinic-like lesions. In view of the low toxicity and mutagenicity of 3-CPs, DNA photo-oxidation products induced by the photodynamic effect of 3-CPs are likely to be efficiently taken care of by the DNA repair system(s). It is clear that 3-CPs photo-induces several classes of DNA damage, including oxidative damage.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Oxidative DNA damage photo-induced by 3-carbethoxypsoralen and other furocoumarins. Mechanisms of photo-oxidation and recognition by repair enzymes. 247 51

Exposure of the plasmid pBR 322 to the aerobic xanthine oxidase reaction introduced single strand scissions and endonuclease III-sensitive sites. The latter may be residues of thymine glycol. Both forms of DNA damage were completely prevented by superoxide dismutase or catalase, whereas bovine serum albumin was much less effective. Mannitol and benzoate, added as scavengers of HO., and desferrioxamine or diethylene triamine pentaacetate, added to sequester Fe(III), also protected. These results indicate a metal-catalyzed interaction of O2- with H2O2, which produces HO. which, in turn, causes DNA strand scission and oxidation of thymine residues to thymine glycol. Plasmid isolated from aerobically-incubated cells contained more strand scissions and endonuclease III-sensitive sites than did plasmid from anaerobically-incubated cells, and a low molecular weight scavenger of O2- prevented the damage seen with the aerobic cells. Genetic defects in AP endonucleases rendered E. coli more susceptible to the dioxygen-dependent lethality of plumbagin, which mediates O2- production. Similarly, plasmid DNA, within the endonuclease-deficient cells, exhibited more strand scissions and endonuclease III-sensitive sites upon aerobic exposure to plumbagin than did endonuclease-sufficient cells, and a low molecular weight scavenger of O2- was protective. These results are consistent with the conclusions that strand scissions and formation of endonuclease III-sensitive sites are among the consequences of exposure of DNA to O2- plus H2O2, both in vitro and in vivo.
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PMID:Formation of endonuclease III-sensitive sites as a consequence of oxygen radical attack on DNA. 254 64

Ultraviolet irradiation of DNA produces a variety of pyrimidine base damages. The activities of Escherichia coli endonuclease III and a human lymphoblast endonuclease that incises ultraviolet-irradiated DNA at modified cytosine moieties were compared. Both the bacterial and human enzymes release this cytosine photoproduct as a free base. These glycosylase activities are linear with times of reaction, quantities of enzyme, and irradiation dosages of the substrates. Both enzyme activities are similarly inhibited by the addition of monovalent and divalent cations. Analysis by DNA sequencing identified loci of endonucleolytic incision as cytosines. These are neither cyclobutane pyrimidine dimers, 6-(1,2-dihydro-2-oxo-4-pyrimidinyl)-5-methyl-2,4(1H,3H)-pyrimidinediones, nor apyrimidinic sites. This cytosine photoproduct is separable from unmodified cytosine by high-performance liquid chromatography. This separation should facilitate identification of this modified cytosine and elucidation of its biological significance.
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PMID:Cytosine photoproduct-DNA glycosylase in Escherichia coli and cultured human cells. 265 93

The biological processing of thymine ring saturation and fragmentation products is summarized in Table 1. The ring saturation product, thymine glycol, is a block to in vitro DNA synthesis, whereas the ring saturation product, dihydrothymine, is not. Both these lesions are recognized in vitro by endonucleases III and VIII. Since thymine glycol is a replicative block, it is a lethal lesion in vivo. The excision repair process for removal of thymine glycols from DNA is initiated in vivo by endonuclease III and is followed by the action of either exonuclease III or endonuclease IV. Thymine glycol is very efficiently bypassed by translesion bypass in both single and double stranded DNA, however, because thymine glycol templates an adenine (A) and retains pairing characteristics, it is at best a weakly mutagenic lesion. The thymine ring fragmentation product, urea, and apurinic/apyrimidinic (AP) sites are both strong blocks to in vitro DNA synthesis. Both are substrates in vitro for endonucleases III, IV, VIII and IX as well as exonuclease III. Both are lethal lesions in single stranded and double stranded phage transfecting DNA. The excision repair of urea residues and AP sites is initiated in vivo by either exonuclease III or endonuclease IV. Neither of these noninstructive lesions are efficiently bypassed by UV-induced translesion bypass, however, when bypass occurs mutations result. beta-ureidoisobutylic acid is also a block to DNA synthesis in vitro. DNA containing this lesion is a substrate for endonucleases VIII and IX. The biological processing of this ring open thymine fragmentation product has yet to be determined. Thus, these ring saturation and fragmentation products of thymine have provided a point of departure for understanding the biological processing of modified bases with altered pairing and/or stacking properties.
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PMID:Processing of ring saturation and fragmentation products of DNA thymine in Escherichia coli. 266

The gene which codes for endonuclease III of Escherichia coli has been sequenced. The nth gene was previously subcloned and defined as the gene which led to overproduction of endonuclease III when present on a multicopy plasmid and which created a deficiency in endonuclease III activity when mutated. The nth gene was sequenced and translated into a predicted polypeptide. The molecular weight (23,546), the amino-terminal amino acid sequence, and the amino acid composition of the polypeptide predicted from the nucleotide sequence are excellent agreement with those same properties determined for the purified protein. Thus, the nth gene is the structural gene for endonuclease III. Inspection of the nucleotide sequence reveals that there is an open reading frame immediately upstream of the nth gene, suggesting that it might be part of an operon. There is a region of dyad symmetry which could form a hairpin stem and loop structure if transcribed into RNA characteristic of a rho-dependent terminator downstream from the nth gene. The nth gene of Escherichia coli has been cloned onto a lambda PL expression vector which yields approximately 300-fold overproduction of endonuclease III. We have purified the enzyme to apparent homogeneity using two chromatographic steps. Our purification scheme allowed the preparation of 117 mg of protein from 190 g of E. coli with a 70% yield. The purified protein has both AP endonuclease activity and DNA N-glycosylase activity. The protein has a Stokes radius of 2.25 nm, a sedimentation coefficient of 2.65 S, a molecular weight of 26,300 in the native state and 27,300 in the denatured state, and a frictional ratio of 1.13.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Purification and characterization of Escherichia coli endonuclease III from the cloned nth gene. 266 55

The wavelength dependence of an ultraviolet irradiation of the DNA substrate for a human endonuclease was determined. Sites of DNA incision for all UVB and UVC wavelengths examined were at cytosines which were neither cyclobutane pyrimidine dimers nor 6-4'-(pyrimidin-2-one)pyrimidines. The optimal wavelengths for formation of these cytosine photoproducts were between 270 and 295 nm. This human endonuclease therefore has a similar ultraviolet substrate specificity to endonuclease III.
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PMID:Wavelength dependence of DNA incision by a human ultraviolet endonuclease. 273 70

We have compared the sites of nucleotide incision on DNA damaged by oxidizing agents when cleavage is mediated by either Escherichia coli endonuclease III or an endonuclease present in bovine and human cells. E. coli endonuclease III, the bovine endonuclease isolated from calf thymus, and the human endonuclease partially purified from HeLa and CEM-C1 lymphoblastoid cells incised DNA damaged with osmium tetroxide, ionizing radiation, or high doses of UV light at sites of pyrimidines. For each damaging agent studied, regardless of whether the E. coli, bovine, or human endonuclease was used, the same sequence specificity of cleavage was observed. We detected this endonuclease activity in a variety of human fibroblasts derived from normal individuals as well as individuals with the DNA repair deficiency diseases ataxia telangiectasia and xeroderma pigmentosum. The highly conserved nature of such a DNA damage-specific endonuclease suggests that a common pathway exists in bacteria, humans, and other mammals for the reversal of certain types of oxidative DNA damage.
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PMID:A highly conserved endonuclease activity present in Escherichia coli, bovine, and human cells recognizes oxidative DNA damage at sites of pyrimidines. 303 65

Escherichia coli endonuclease III is not an endonuclease. It breaks the C3'-O-P bond 3' to an AP site in DNA by catalysing a beta-elimination and not a hydrolysis. Therefore, it is a phosphoric monoester-lyase.
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PMID:[Endonuclease III of Escherichia coli and the repair of oxidized thymines and AP sites]. 303 21

Endonuclease III isolated from Escherichia coli has been shown to have both N-glycosylase and apurinic/apyrimidinic (AP) endonuclease activities. A nicking assay was used to show that the enzyme exhibited a preference for form I DNA when DNA containing thymine glycol was used as a substrate. This preference was reduced or eliminated either when the DNA was relaxed or when the type of damage was altered to urea residues or AP sites. The combined N-glycosylase/AP endonuclease activity was at least 10-fold higher than the AP endonuclease activity alone when urea-containing DNA was used as a substrate as compared to AP DNA. When DNA containing thymine glycol was used as a substrate, the combined N-glycosylase/AP endonuclease activity was about 2-fold higher than the AP endonuclease activity. Yet, when DNA containing thymine glycol or urea was used as substrate, no apurinic sites remained. Furthermore, magnesium selectively inhibited endonuclease III activity when AP DNA was used as a substrate but had no effect when DNA containing either urea or thymine glycol was used as substrate. These data suggest that both the N-glycosylase and AP endonuclease activities of endonuclease III reside on the same molecule or are in very tight association and that these activities act in concert, with the N-glycosylase reaction preceding the AP endonuclease reaction.
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PMID:Mechanism of action of Escherichia coli endonuclease III. 332 18

Photoalkylation, the ultraviolet irradiation of DNA with isopropanol and di-tert-butylperoxide, causes a variety of base alterations. These include 8-(2-hydroxy-2-propyl)guanines, 8-(2-hydroxy-2-propyl)adenines and thymine dimers. An E. coli endonuclease against photoalkylated DNA was assayed by conversion of superhelical PM2 phage DNA to the nicked form. Enzyme activities were compared between extracts of strain BW9109 (xth-), lacking exonuclease III activity, and strain BW434 (xth-,nth-), deficient in both exonuclease III and endonuclease III. The endonuclease level in the double mutant against substrate photoalkylated DNA was under 20% of the activity in the mutant lacking only exonuclease III. Irradiation of the DNA substrate in the absence of isopropanol did not affect the activity in either strain. Analysis by polyacrylamide gel electrophoresis identified the sites of DNA cleavage by purified E. coli endonuclease III as cytosines, both in DNA irradiated at biologically significant wavelengths and in photoalkylated DNA. Neither 8-(2-hydroxy-2-propyl)purines, pyrimidine dimers, uracils nor 6-4'-(pyrimidin-2'-one)pyrimidines were substrates for the enzyme.
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PMID:Photoalkylated DNA and ultraviolet-irradiated DNA are incised at cytosines by endonuclease III. 352 39


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