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)

A cell-free system for the study of viral DNA replications was developed by the isolation of a nuclear membrane fraction "DNA replication complex" from adenovirus 2-infected human KB cells late after infection. This complex which possesses both DNA polymerase activity and a virus-specific endonuclease synthesizes exclusively virus-specific DNA sequences in vitro by a semiconservative mechanism. Analysis by rate zonal sedimentation in alkaline sucrose gradients showed that the products of the reaction are small DNA chains approximately 6 to 9 S, presumably "Okazaki intermediates," that are not sealed under our in vitro conditions. Analysis by rate zonal sedimentation in neutral sucrose gradients showed that labeled viral DNA fragments are hydrogen bonded to viral 18 S DNA segments, 0.25 the size of the linear, viral 31 S DNA genome. The 18 S DNA is probably a specific cleavage product of the viral endonuclease found in the replication complex and could represent intermediates in viral DNA replication or degradation products.
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PMID:Adenovirus deoxyribonucleic acid replication. II. Synthesis of viral deoxyribonucleic acid in vitro by a nuclear membrane fraction from infected KB cells. 23 46

An mRNA fraction coding for hexon polypeptide, the major virion structural protein, was purified by gel electrophoresis from extracts of adenovirus 2-infected cells late in the lytic cycle. The mRNA sequences in this fraction were mapped between 51.7 and 61.3 units on the genome by visualizing RNA-DNA hybrids in the electron microscope. When hybrids of hexon mRNA and single-stranded restriction endonuclease cleavage fragments of viral DNA were visualized in the electron microscope,branched forms were observed in which 160 nucleotides of RNA from the 5' terminus were not hydrogen bonded to the single-stranded DNA. DNA sequences complementary to the RNA sequences in each 5' tail were found by electron microscopy to be located at 17, 20, and 27 units on the same strand as that coding for the body of the hexon mRNA. Thus, four segments of viral RNA may be joined together during the synthesis of mature hexon mRNA. A model is presented for adenovirus late mRNA synthesis that involves multiple splicing during maturation of a larger precursor nuclear RNA.
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PMID:Spliced segments at the 5' terminus of adenovirus 2 late mRNA. 26 80

The linear duplex replicative form (RF) DNA of the parvovirus H-1 has been characterized with respect to cleavage by the bacterial restriction endonuclease of Escherichia coli, EcoRI. RF DNA has a single cleavage site 0.22 genome length from the left end of the molecule. The molecular weight of H-1 RF DNA determined by gel electrophoresis is 3.26 X 10(6). H-1 RF DNA has been found to dimerize by hydrogen-bounded linkage at the molecular left end, and in some molecules the viral strand is covalently linked to the complementary strand. Some 10% of monomeric RF DNA also has a covalent linkage between the viral and complementary strands at the left end. The EcoRI-B fragment, containing the left end of the RF molecule, appears to be a replication terminus by its labeling characteristics for both RF and progeny DNA synthesis. These findings suggest that the left end of H-1 RF DNA has some type of "turn-around" structure and that this end is not an origin for DNA synthesis.
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PMID:Replication process of the parvovirus H-1. VI. Characterization of a replication terminus of H-1 replicative-form DNA. 85 76

The effects of substituents at position 5 in the pyrimidine ring of a variety of phage DNAs upon EcoRI endonuclease and methylase activities have been examined. The replacement of cytidine in DNA with glucosylated hydroxymethylcytidine confers resistance to cleavage by the EcoRI endonuclease. Substitution of thymidine in DNA by hydroxy-methyluridine(a change in the methyl at position 5 of thymidine for a hydroxymethyl) lowers the maximal velocity of endonucleolytic cleavage 20-fold, but has no detectable effect upon the Km. Substitution of thymidine in DNA by uridine (a change in the methyl at position 5 of thymidine for a hydrogen atom) has no effect upon either the maximal velocity or the Km. The effect of these modifications upon EcoRI methylase activity was markedly different. DNA containing glucosylated hydroxymethylcytidine is methylated as well as normal DNA. DNA containing uridine or hydroxy-methyluridine, in place of thymidine, is much more poorly methylated than normal DNA. These different sensitivities of the EcoRI endonuclease and methylase to modifications in the pyrimidine rings of DNA suggest there are significant differences in the manner by which these enzymes recognize and bind to the canonical EcoRI sequence.
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PMID:EcoRI cleavage and methylation of DNAs containing modified pyrimidines in the recogintion sequence. 86 78

If RNA is extracted from the ribosomes which had been isolated from frozen-thawed tissue of Galleria mellonella, the 28 S RNA, when heated or treated with urea, dissociates into seven different species of polynucleotide fragments. They were designated as R1, R2, R3, R4, R5, R6, and R7, whose molecular weights were estimated to be 1.15x10-6, 0.75x10-6, 0.55x10-6, 0.40x10-6, 0.30x10-6, 0.25x10-6, 0.20x10-6 daltons, respectively. It is likely that R1 and R5 arise from a single nick in original 38 S rRNA. Experiments with isolated R1 suggest that it is made up of a hydrogen-bonded complex of R2 and R4. R5 is a complex of R6 and an unidentified species, X. It is suggested that these fragments result from nicks which are introduced, secondarily, in the phosphodiester bonds by an endogenous endonuclease(s). Since the secondary nicks are limited in number and located in specific points of the molecule, it appears that the reaction is quite specific. It was also shown that the 28 S aphid RNA, which apparently lacks the primary nick, is susceptible to nicking.
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PMID:Polynucleotide fragments from the 28S ribosomal RNA of insects. 112 45

We describe here a new method for the electron microscopic mapping of sequence homology in nucleic acids. Specific segments of the T7 chromosome have been isolated following digestion with the restriction endonuclease from Hemophilus aegyptious (Haey). Denatured segments are annealed to the l-strand of T7 DNA; treatment of the hybrid with glyoxal allows only guanosine residues in the single-chain region to the reacted, producing an adduct which will no longer hydrogen bond with its complement on the r-strand. When the segment is displaced and the glyoxalated l-strand allowed to renature with the r-strand, "H" shaped structures are produced in which the duplex region corresponds to the position of sequence homology with the segment. The conditions employed for glyoxalation do not detectably disrupt duplex regions as small as 400 base pairs. This procedure should be generally useful for observing sequence homology in more complex DNA molecules containing duplex regions which can be specifically enriched for and their arrangement determined by electron microscopy.
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PMID:A new method for mapping nucleic acid sequence homology by electron microscopy. 113 34

The culture medium of Pseudomonas BAL 31 contains endonuclease activities which are highly specific for single-stranged DNA and for the single-stranded or weakly hydrogen-bonded regions in supercoiled closed circular DNA. Exposure of nicked DNA to the culture medium results in cleavage of the strang opposite the sites of preexisting single-strand scissions. At least some of the linear duplex molecules derived by cleavage of supercoiled closed circular molecules contain short single-stranded ends. Single-strand scissions are not introduced into intact, linear duplex DNA or unsupercoiled covalently closed circular DNA. Under these same reaction conditions, 0X174 phage DNA is extensively degraded and PM2 form I DNA is quantitatively converted to PM2 form III linear duplexes. Prolonged exposure of this linear duplex DNA to the concentrated culture medium reveals the presence of a double-strand exonuclease activity that progressively reduces the average length of the linear duplex. These nuclease activities persist at ionic strengths up to 4 M and are not eliminated in the presence of 5% sodium dodecyl sulfate. Calcium and magnesium ion are both required for optimal activity. Although the absence of magnesium ion reduces the activities, the absence of calcium ion irreversibly eliminates all the activities.
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PMID:Extracellular nucleases of Pseudomonas BAL 31. I. Characterization of single strand-specific deoxyriboendonuclease and double-strand deoxyriboexonuclease activities. 117 26

A mutant allele of the Escherichia coli nfo gene encoding endonuclease IV, nfo-186, was cloned into plasmid pUC18. When introduced into an E. coli xthA nfo mutant, the gene product of nfo-186 complemented the hypersensitivity of the mutant to methyl methanesulfonate (MMS) but not to hydrogen peroxide (H2O2) and bleomycin. These results suggest that the mutant endonuclease IV has normal activity for repairing DNA damages induced by MMS but not those induced by H2O2 and bleomycin. A missense mutation in the cloned nfo-186 gene, in which the wild-type glycine 149 was replaced by aspartic acid, was detected by DNA sequencing. The wild-type and mutant endonuclease IV were purified to near homogeneity, and their apurinic (AP) endonuclease and 3'-phosphatase activities were determined. No difference was observed in the AP endonuclease activities of the wild-type and mutant proteins. However, 3'-phosphatase activity was dramatically reduced in the mutant protein. From these results, it is concluded that the endonuclease IV186 protein is specifically deficient in the ability to remove 3'-terminus-blocking damage, which is required for DNA repair synthesis, and it is possible that the lethal DNA damage by H2O2 is 3'-blocking damage and not AP-site damage.
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PMID:A mutant endonuclease IV of Escherichia coli loses the ability to repair lethal DNA damage induced by hydrogen peroxide but not that induced by methyl methanesulfonate. 128 Feb 56

The responses of Escherichia coli to X rays and hydrogen peroxide were examined in mutants which are deficient in one or more DNA repair genes. Mutant cells deficient in either exonuclease III (xthA) or endonuclease IV (nfo) had normal resistance to X rays, but an xthA-nfo double mutant showed a sensitivity increased over that of either parental strain. A DNA polymerase I mutant (polA) was more sensitive than the xthA-nfo mutant. Cells bearing mutations in all of the polA, xthA, and nfo genes were more sensitive to X rays than polA and xthA-nfo mutants. Similar repair responses were obtained by exposing these mutant cells to hydrogen peroxide, with the exception of the xthA mutant, which was hypersensitive to this agent. The DNA polymerase III mutant (polC(Ts)) was slightly more sensitive to the agents than the wild-type strain at the restrictive temperature. The sensitivity of the polC-xthA-nfo mutant to X rays and hydrogen peroxide was greater than that of polC but almost the same as that of the xthA-nfo mutant. From these results it appears that there are at least four repair pathways, the DNA polymerase I-, exonuclease III/endonuclease IV and DNA polymerase I-, exonuclease III/endonuclease IV and DNA polymerase III-, and exonuclease III/endonuclease IV-dependent pathways, for the repair of oxidative DNA damages in E. coli.
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PMID:Multiple pathways for repair of oxidative DNA damages caused by X rays and hydrogen peroxide in Escherichia coli. 128 65

Cigarette smoke can cause DNA single strand breaks in cultured human lung cells (T. Nakayama et al., Nature, 314 (1985) 462-464) but the mechanisms behind this DNA damage have not been clearly elucidated. In the present study we have investigated the possibility that one of the major constituents in cigarette smoke, hydroquinone, may be important for mediating smoke-induced DNA damage in the human epithelial lung cell line, A 549, and the mechanisms behind this damage. Cells were exposed to cigarette smoke, hydrogen peroxide, or hydroquinone, in the absence and presence of different inhibitors, and the resulting DNA damage was assessed either as DNA single strand break formation or formation of the oxidative DNA adduct, 8-hydroxydeoxyguanosine. It was found that (i) exposure to cigarette smoke, hydrogen peroxide or hydroquinone causes a rapid decrease in the intracellular thiol level and a considerable DNA single strand break formation, (ii) the formation of DNA single strand breaks in cells exposed to cigarette smoke is inhibited by catalase, dimethylthiourea, and o-phenantroline, suggesting that hydroxyl radicals generated from iron-catalyzed hydrogen peroxide dissociation are involved in the DNA damage, (iii) hydroquinone causes considerable DNA strand break formation that is blocked by aurintricarboxylic acid, an inhibitor of endonuclease activation, and by BAPTA, an intracellular calcium chelator, (iv) addition of hydroquinone to a smoke condensate greatly enhances its ability to cause DNA single strand breaks, and (v) smoke, but not hydroquinone, causes formation of 8-hydroxydeoxyguanosine, a DNA damage product induced by the action of hydroxyl radicals on the DNA base, deoxyguanosine. These findings suggest that the ability of cigarette smoke to cause DNA single strand breaks in cultured lung cells is due to mechanisms involving hydroxyl radical attack on DNA and endonuclease activation. They also suggest that hydroquinone is an important contributor to the DNA damaging effect of cigarette smoke on human lung cells.
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PMID:Cigarette smoke-induced DNA damage in cultured human lung cells: role of hydroxyl radicals and endonuclease activation. 130 85


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