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 mutant (designated mec(-)) has been isolated from Escherichia coli C which has lost DNA-cytosine methylase activity and the ability to protect phage lambda against in vivo restriction by the RII endonuclease. This situation is analogous to that observed with an E. coli K-12 mec(-) mutant; thus, the E. coli C methylase appears to have overlapping sequence specificity with the K-12 and RII enzymes; (the latter methylases have been shown previously to recognize the same sequence). Covalently closed, supertwisted double-standed DNA (RFI) was isolated from C mec(+) and C mec(-) cells infected with bacteriophage phiX174. phiX. mec(-) RFI is sensitive to in vitro cleavage by R.EcoRII and is cut twice to produce two fragments of almost equal size. In contrast, phiX.mec(+) RFI is relatively resistant to in vitro cleavage by R.EcoRII. R.BstI, which cleaves mec(+)/RII sites independent of the presence or absence of 5-methylcytosine, cleaves both forms of the RFI and produces two fragments similar in size to those observed with R. EcoRII. These results demonstrate that phiX.mec(+) RFI is methylated in vivo by the host mec(+) enzyme and that this methylation protects the DNA against cleavage by R.EcoRII. This is consistent with the known location of two mec(+)/ RII sequences (viz., [Formula: see text]) on the phiX174 map. Mature singlestranded virion DNA was isolated from phiX174 propagated in C mec(+) or C mec(-) in the presence of l-[methyl-(3)H]methionine. Paper chromatographic analyses of acid hydrolysates revealed that phiX.mec(+) DNA had a 10-fold-higher ratio of [(3)H]5-methylcytosine to [(3)H]cytosine compared to phiX.mec(-). Since phiX.mec(+) contains, on the average, approximately 1 5-methylcytosine residue per viral DNA, we conclude that methylation of phiX174 is mediated by the host mec(+) enzyme only. These results are not consistent with the conclusions of previous reports that phiX174 methylation is mediated by a phage-induced enzyme and that methylation is essential for normal phage development.
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PMID:In vivo methylation of bacteriophage phi X174 DNA. 15 62

The purified A protein and A* protein of bacteriophage phi X174 have been tested for endonuclease activity on single stranded viral phi X174 DNA. The A protein (55.000 daltons) nicks single-stranded DNA in the same way and at the same place as it does superhelical RFI DNA, at the origin of DNA replication. The A* protein (37.000 daltons) can cleave the single-stranded viral DNA at many different sites. It has however a strong preference for the origin of replication. Both proteins generate 3'OH ends and blocked 5' termini at the nick site.
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PMID:Cleavage of single-stranded DNA by the A and A* proteins of bacteriophage phi X174. 16 May 44

The mechanism of EcoRI endonuclease is substrate dependent. At 37 degrees dissociation of the enzyme-Form II DNA intermediates of ColE1 DNA and bacteriophage G4 RFI DNA is negligible. Therefore, both DNA strands with in the EcoRI sequence are cleaved during a single binding event. However, double strand cleavage of SV40 DNA occurs without dissociation of the enzyme in only 75% of the catalytic events. This mechanistic difference presumably reflects sequence differences about the EcoRI sites of these DNA's.
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PMID:Substrate dependence of the mechanism of EcoRI endonuclease. 21 92

Preparations containing DNA gyrase activity Gellert, M., Mizuchi, K., O'Dea, M.H. & Nash, H.A. (1976) Proc. Natl. Acad. Sci. USA 73, 3872-3876] have been extensively purified from Escherichia coli. Such fractions, in the presence of ATP and Mg2+, catalyze supertwisting of relaxed circular double-stranded DNA replicative forms of a number of DNAs that results in the formation of superhelical replicative forms. Relaxed phiX174 replicative form (phiX RFIV) is not attacked by the A protein endonuclease coded for by the phiX DNA genome. After exposure to preparations of DNA gyrase, the relaxed phiX174 replicative form is converted to phiX RFI which can then be attacked by the phiX gene A protein and participate in replication of duplex phiX DNA.
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PMID:Role of DNA gyrase in phiX replicative-form replication in vitro. 26 16

Bacteriophage fd gene II-protein was characterized as an endonuclease which specifically nicked supercoiled replicative form (RF) of filamentous phages in the viral strand. No other supercoiled DNAs tested were attacked by the enzyme, nor were doubly closed fd RF in the relaxed state nor phage fd single strands. Maximal activity was found at pH 8.5 and 80 mM KCl using fd RFI of physiological superhelicity. Mg2+, but no other cofactor, was required for the cleavage reaction. A sealing activity was found to be associated with the enzyme. At a higher concentration of Mg2+ up to 40% of the reaction products were found as doubly closed relaxed fd RF. The protein was not found to be tightly attached to the cleaved strand.
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PMID:Bacteriophage fd gene II-protein. II. Specific cleavage and relaxation of supercoiled RF from filamentous phages. 38 92

A formaldehyde denaturation map of the replicative form of phiX174 DNA is obtained. The RFI DNA was converted into a linear state by restriction endonuclease pst I which introduces into this DNA a single double-stranded break. The map has four clear-cut peaks. Their positions excellently correlate with the peak positions on the map of equilibrium denaturation theoretically obtained earlier from the known nucleotide sequence of phiX174 DNA. The sequence is also used for a calculation of the maps of smoothed AT-content. The maxima on these maps correlate well with the peaks on the denaturation maps. To reveal the causes of a good correlation between the experimental formaldehyde and theoretical equilibrium denaturation maps, the theoretical formaldehyde denaturation maps are calculated for different conditions (temperature, formaldehyde concentration) using the detailed theory of DNA interaction with formaldehyde developed earlier.
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PMID:Denaturation maps of DNA: experimental and theoretical maps of phiX174 DNA. 56 10

The activity of damage-dependent endonuclease in mouse plasmacytoma cells (line MPC-11) has been studied using damaged phi X 174 RFI DNA as substrate. The DNA was treated with ultraviolet light, acid, or osmium tetroxide to introduce different types of lesions. Ultraviolet light-damaged DNA was cleaved at approx. 1.1 sites per 35 thymine-containing dimers by the extract, which indicates no specificity towards this type of lesion. The acid-treated DNA, which contains apurinic sites, was enzymatically broken in every alkalilabile site and this strongly suggests the presence of an apurinic-specific endonuclease activity in the nuclear extract. The activity which acts on ultraviolet-irradiated DNA and that which acts on acid-treated DNA have different specificities as shown by their salt requirements and the extent to which they are stimulated by magnesium. While the ultraviolet-endonuclease activity was very little affected by reducing the KCl concentration, the apurinic-specific activity was almost completely abolished. Osmium tetroxide renders the DNA an excellent substrate for endonucleolytic activity in the mouse cell extract. The response to KCl and MgCl2 of the osmium tetroxide-specific endonuclease activity is qualitatively similar to that of the endonuclease activity, which acts on ultraviolet-irradiated DNA. Treatment of DNA with osmium tetroxide is known to produce 5,6-dihydroxydihydrothymine which is a minor photoproduct in DNA after irradiation, suggesting that the ultraviolet-specific endonuclease activity acts upon this lesion.
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PMID:Endonuclease activities from a permanently established mouse cell line that act upon DNA damaged by ultraviolet light, acid and osmium tetroxide. 69 23

We have analyzed the susceptibility of the deoxyribonucleic acid (DNA) of phage fd replicative form (RF) and of Escherichia coli to in vitro cleavage by purified RII restriction endonuclease (R. Eco RII). The results are summarized as follows: (i) fd, mec- RFI, isolated from infected E. coli K-12 mec- bacteria (a mutant strain lacking DNA-cytosine methylase activity), is cleaved into at least two fragments, whereas fd. mec+ RFI, isolated from the parental mec+ strain, is not cleaved. (ii) E. coli mec- DNA is extensively degraded, whereas mec+ DNA-cytosine methylase acts as an RII modification enzyme.
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PMID:In vivo methylation by Escherichia coli K-12 mec+ deoxyribonucleic acid-cytosine methylase protects against in vitro cleavage by the RII restriction endonuclease (R. Eco RII). 77 Apr 62

Five peaks of endonuclease activity showing a preference for ultraviolet-damaged DNA have been chromatographically identified from extracts of Micrococcus luteus. They are numerically designated as I to V in order of their elution from phosphocellulose (Whatman P-11) columns. The first two of these peaks have been highly purified by a combination of gel filtration and affinity chromatography and are catalytically homogeneous judging from their effect on transforming DNAs. Peak I, which has an isoelectric point of 4.7, is heat-stable, requires high ionic strength for optimal activity, acts with equal facility on ultraviolet-irradiated native and denatured DNA, and has been designated as Py pyrimidine dimer Py correndonuclease I. Peak II which has a pI value of 8.7, is heat-labile, is inhibited by high ionic strength, acts on ultraviolet-irradiated native but not denatured DNA, and has been designated as Py pyrimidine dimer Py correndonuclease II. Both enzymes are inhibited by Ca2+ and Zn2+, do not show any cofactor or sulfhydryl requirement, act optimally between pH 7.0 and 7.4, and have molecular weights between 11,000 and 15,000. Py pyrimidine dimer Py correndonuclease I requires a dose about 1.6 times that for Py pyrimidine dimers Py correndonuclease II for incision saturation of irradiated phiX174 RFI DNA.
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PMID:Micrococcus luteus correndonucleases. I. resolution and purification of two endonucleases specific for DNA containing pyrimidine dimers. 89 8

We have studied excision-repair of UV-irradiated phiX174 RFI DNA in vitro with UV-specific endonuclease from Micrococcus luteus (UV-endo), DNA polymerase I from Escherichia coli and DNA ligase from phage T4 infected E. coli. Excision-repair was measured a) by physico-chemical methods, i.e. by determination of the conversion of RF I DNA into RF II DNA by UV-endo and by the subsequent conversion of RF II DNA ligase, b) by biological methods i. e. by measuring the ability of the reaction product to form phages upon incubation with spheroplasts from the appropriate strains of E. coli. Using the first method, we have shown, that more than 90% of the pyrimidine dimers can be repaired in vitro; with the latter method we have shown, that the molecules which are repaired as defined by method a) have regained full biological activity. Exonuclease III was found to be not essential for excision-repair in vitro and also did not stimulate repair. From this result we conclude that UV-endo generates 3'OH endgroups, in agreement with results obtained by Hamilton et al. (1974). The usefulness of the method presented in this paper with regard to the study of excision-repair is discussed.
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PMID:Physico-chemical and biological study of excision-repair of UV--irradiated phiX174 RF DNA in vitro. 105 35


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