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)

A deoxyribonuclease has been purified 570-fold from the 14-day-old chick embryos. The purified enzyme requires Mg2+ or Mn2+ ions for maximum activity. The optimum pH is 9.0 in 20 mM Tris-HCl buffer. Its isoelectric point is 6.7. NaCl and N-ethylmaleimide strongly inhibit the reaction. An apparent molecular weight of 45,000 is determined by sedimentation in a glycerol density gradient. The enzyme hydrolyzes denatured DNA 50 to 100 times more rapidly than duplex DNA. RNA and synthetic polyribonucleotides are not substrate for the enzyme. DNase A catalyzes the endonucleolytic and exonucleolytic cleavages of single-stranded DNA. The enzyme produces DNA fragments having 70 to 100 nucleotides long at early time of reaction and then degrades these DNA fragments to acid-soluble materials, of which more than 70% is mononucleotides. In the exonucleolytic attack, the enzyme initiates hydrolysis of a single-stranded DNA from 5' to 3' direction. Chick embryo DNA-binding protein gives an intensive effect on the DNase A reaction by inhibiting the endonuclease activity rather than exonuclease activity under the standard assay conditions.
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PMID:Deoxyribonuclease A of chick embryo. Partial purification and characterization of the enzyme. 682 17

A sensitive endonuclease assay was used to study the fate of pyrimidine dimers introduced by ultraviolet irradiation into the nuclear deoxyribonucleic acid of the cellular slime mold Dictyostelium discoideum. Analysis of the frequency of T4 endonuclease V-induced single-strand breaks by alkaline sucrose gradient sedimentation showed that strain NC4 (rad+) removed greater than 98% of the dimers induced by irradiation at 40 J/m2 (254 nm) within 215 min after irradiation. HPS104 (radC44), a mutant sensitive to ultraviolet irradiation, removed 91% under these conditions, although at a significantly slower rate than NC4: only 8% were removed during the 10- to 15-min period immediately after irradiation, whereas NC4 excised 64% during this interval. HPS104 thus appears to be deficient in the activity(ies) responsible for rapidly incising ultraviolet-irradiated nuclear deoxyribonucleic acid at the sites of pyrimidine dimers.
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PMID:Excision of pyrimidine dimers from nuclear deoxyribonucleic acid in ultraviolet-irradiated Dictyostelium discoideum. 696 95

An endodeoxyribonuclease has been purified to near homogeneity from rat small intestinal mucosa by a procedure involving Con A-Sepharose affinity chromatography. During the initial steps of purification, the presence of 5 mM CaCl2 was essential for stability of the enzyme activity. The enzyme has a molecular weight of 32 000 and an isoelectric point of 4.7. NaCl, sulfhydryl reagents, and iodoacetate strongly inhibited the reaction, but tRNA did not. The enzyme required divalent cations for activity and had a pH optimum of pH 6.2 with Co2+ and pH 7.7 with Mn2+. In both optimum conditions, the enzyme hydrolyzed native DNA more rapidly than denatured DNA, and the average chain lengths of limit digestion products of native and denatured DNA were 8 and 10, respectively, at pH 6.2 and 9 and 11, respectively, at pH 7.7. The enzyme activity to produce acid-soluble fractions from linear DNA substrate was similar in the two optimum conditions, but the activity to nick double-stranded, superhelical circular DNA substrate was significantly higher at pH 6.2 than at pH 7.7. The endonuclease formed single-strand breaks making 5'-phosphoryl and 3'-hydroxyl termini, and deoxythymidine was present at the 5' termini with a frequency of about 50% in both optimum conditions. Bovine pancreatic DNase I antibody and G-action inhibited the enzyme activity. Thus this endonuclease is classified as a DNase I.
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PMID:Purification and properties of a neutral endodeoxyribonuclease from rat small intestinal mucosa. 707 91

Deoxyribonuclease activities were examined in isoelectric focusing fractions of non-histone, chromatin-associated and nucleoplasmic proteins of isolated normal human lymphoblastoid and mouse melanoma cell nuclei using parallel procedures. A very similar series of eight DNA endonucleases, each active on calf thymus DNA and containing no exonuclease activity, were found in the chromatin proteins of both cell lines. Several differences were observed: an activity in human cells at pI 6.6 was absent from murine cells, and there was an increased activity in mouse cells at pI 4.4 and a decreased activity at pI 7.3, as compared with corresponding human cell activities. Assay of these fractions against supercoiled, circular phage PM2 DNA showed greater activity among the fractions with acidic pI valves and slightly lower activities in the murine cells than in the human cells. Analysis of the nucleoplasmic fractions showed a series of DNA endonuclease and exonuclease activities which were again very similar between the two cell lines, although greater endonuclease activity at pI 4.4 occurred in mouse than in human nucleoplasm. These results demonstrate an entire series of deoxyribonuclease activities in both chromatin and nucleoplasm which are nearly identical in two very different mammalian cell lines, suggesting that many of these enzymes are ubiquitous in mammalian cell nuclei.
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PMID:Nuclear deoxyribonuclease activities in human lymphoblastoid and mouse melanoma cells. A comparative study. 715 90

DNA-repair characteristics of xeroderma pigmentosum belonging to complementation group F were investigated. The cells exhibited an intermediate level of repair as measured in terms of (1) disappearance of T4 endonuclease-V-susceptible sites from DNA, (2) formation of ultraviolet-induced strand breaks in DNA, and (3) ultraviolet-induced unscheduled DNA synthesis during post-irradiation incubation. The impaired ability of XP3YO to perform unscheduled DNA synthesis was restored, to half the normal level, by the concomitant treatment with T4 endonuclease V and ultraviolet-inactivated Sendai virus. It is suggested that xeroderma pigmentosum cells of group F may be defective, at least in part, in the incision step of excision repair.
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PMID:Repair of ultraviolet radiation damage in xeroderma pigmentosum cells belonging to complementation group F. 720 91

The transfer of tetracycline resistance among strains of Clostridium difficile is described. Transfer occurred by a conjugation-like event that was insensitive to deoxyribonuclease, could not be mediated by donor culture filtrates or chloroform-treated donor cultures, and required cell-to-cell contact. Tetracycline-resistant progeny recovered from matings displayed a resistance phenotype identical to that of the donor in level of resistance, constitutive expression, and transmissibility. Although the original tetracycline-resistant donor contained 5 x 10(6)- and 22 x 10(6)-dalton plasmids, standard physical analyses of antibiotic-resistant transconjugants revealed no plasmid deoxyribonucleic acid molecules in common with the donor strain. Furthermore, tetracycline-susceptible derivatives of the original donor always possessed a plasmid complement identical to that of the resistant parental strain as determined by restriction endonuclease digestion analysis. The results indicate that the tetracycline resistance determinant(s) was not encoded by readily detectable plasmid deoxyribonucleic acid and may be chromosomally located.
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PMID:Transferable tetracycline resistance in Clostridium difficile. 727 Dec 79

An ATP-dependent deoxyribonuclease was isolated from lymphocyte nuclei. The enzyme preparation sediments with about 4 S through sucrose gradients and shows one stainable band after sodium dodecyl sulfate gel electrophoresis. We find three, possibly four, activities associated with the enzyme: a DNA-independent ATPase activity; an ATP-independent endonuclease; an ATP-dependent nuclease which degrades nicked DNA to acid-soluble material; and an unwinding activity producing single-stranded regions in nicked DNA.
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PMID:A lymphocyte ATP-dependent deoxyribonuclease. Isolation and properties. 730 58

Streptococcus pneumoniae R6X was lysogenized with bacteriophage 304 isolated after mitomycin induction of an ungrouped alpha-hemolytic streptococcus. Lysogenized pneumococci lost their capacity to undergo genetic transformation: transformability was restored after cells were spontaneously cured of their prophage. Both lysogens and nonlysogens produced activator substance (competence factor), and both bound deoxyribonucleic acid in a deoxyribonuclease-resistant form. However, nonlysogens retained deoxyribonucleic acid after washing, whereas lysogens did not. The latter did not liberate phage nor (unlike nonlysogens) degrade transforming deoxyribonucleic acid and contained normal levels of endonuclease.
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PMID:Inhibition of transformation in Streptococcus pneumoniae by lysogeny. 736 27

The recognition of 'regular' and 'oxidized' sites of base loss (AP sites) in DNA by various AP endonucleases was compared. Model substrates with regular AP sites (resulting from mere hydrolysis of the glycosylic bond) were produced by damaging bacteriophage PM2 DNA by exposure to low pH; those with AP sites oxidized at the C-4'- and C-1'-position of the sugar moiety by exposure to Fe(III)-bleomycin in the presence of H2O2 and to Cu(II)-phenanthroline in the presence of H2O2 and ethanol, respectively. The results confirmed that AP sites-together with single-strand breaks-are indeed the predominant type of DNA modification in all three cases. For the recognition of 4'-oxidized AP sites, a 400-fold higher concentration of Escherichia coli exonuclease III and between 5-fold and 50-fold higher concentrations of bacteriophage T4 endonuclease V, E. coli endonuclease III and E. coli FPG protein were required than for the recognition of regular AP sites. In contrast, the recognition of 4'-oxidized AP sites by E. coli endonuclease IV was effected by 4-fold lower concentrations than needed for regular AP sites. 1'-oxidized AP sites (generated by activated Cu(II)-phenanthroline) were recognized by endonuclease IV and exonuclease III only slightly (3-fold and 13-fold, respectively) less efficiently than regular AP sites. In contrast, there was virtually no recognition of 1'-oxidized AP sites by the enzymes which cleave at the 3' side of AP sites (T4 endonuclease V, endonuclease III and FPG protein). The described differences were exploited for the analysis of the DNA damage induced by hydroxyl radicals, generated by ionizing radiation or Fe(III)-nitrilotriacetate in the presence of H2O2. The results indicate that both regular and 1'-oxidized AP sites represent only minor fractions of the AP sites induced by hydroxyl radicals.
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PMID:Recognition of oxidized abasic sites by repair endonucleases. 751 77

Although enzymatic photoreactivation of cyclobutyl pyrimidine dimers in DNA is present in almost all organisms, its presence in placental mammals is controversial. We tested human white blood cells for photolyase by using three defined DNAs (supercoiled pET-2, nonsupercoiled bacteriophage lambda, and a defined-sequence 287-bp oligonucleotide), two dimer-specific endonucleases (T4 endonuclease V and UV endonuclease from Micrococcus luteus), and three assay methods. We show that human white blood cells contain photolyase that can photorepair pyrimidine dimers in defined supercoiled and linear DNAs and in a 287-bp oligonucleotide and that human photolyase is active on genomic DNA in intact human cells.
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PMID:Human white blood cells contain cyclobutyl pyrimidine dimer photolyase. 756 7


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