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

The twisting potential of DNA has been determined directly by a method that measures the cyclization probability or j-factor of EcoRI restriction fragments as a function of DNA twist. The cyclization probability is proportional to Kc, the equilibrium constant for cyclization of the restriction fragment via its cohesive ends (Shore et al., 1981). Here we vary the twist of the DNA by making small internal additions to or deletions from a 242 bp EcoRI restriction fragment. A series of 12 DNA molecules has been studied, which range in length from 237 to 254 bp. The cyclization probability is measured from the rates of covalent closure by phage T4 DNA ligase of two systems: (1) a linear restriction fragment in equilibrium with its cyclized form and (2) half molecules (cut by a blunt-end endonuclease) in equilibrium with joined half molecules. The striking result is that, in this DNA size range, the j-factor depends strongly on the fractional twist: the difference between the total helical twist and the nearest integer. Thus j depends in an oscillatory manner on DNA length between 237 and 254 bp with a period of about 10 bp. These data give the free energy of DNA twisting as a function of twist. The curve of j versus DNA length can be fitted to a harmonic twisting potential with a torsional constant of C = 2.4 X 10(-19) erg cm. This value is in reasonable agreement with different estimates of C made by Barkley & Zimm (1979: C = 1.8 X 10(-19) to 4.1 X 10(-19) erg cm) and is somewhat larger than the value obtained resulting from the kinetics of DNA twisting measured by fluorescence depolarization of ethidium intercalated into DNA (C = 1.4 X 10(-19) erg cm; Millar et al., 1982; Thomas et al., 1980) or from spin label studies (Hurley et al., 1982). Our experiments provide a direct measurement of the torsional free energy and they show that the DNA twisting potential is symmetric. Our experiments also indicate that the DNA helix is continuous, or nearly so, in a nicked circle; presumably this happens because the DNA stacking interaction maintains the double helix in register across a single-strand nick. As a consequence, the twist of a singly nicked DNA circle is integral for small (approximately equal to 250 bp) planar DNA circles and there is a change in twist upon cyclization.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Energetics of DNA twisting. I. Relation between twist and cyclization probability. 631 55

The anthracycline antineoplastic agents Adriamycin and N-trifluoroacetyl-Adriamycin-14-valerate were assayed in vivo and in vitro for ability to produce DNA lesions recognized by the UVRABC endonuclease, a DNA repair enzyme of Escherichia coli which recognizes large, bulky lesions in DNA. We found that, while both drugs produce DNA lesions, only the lesions produced by Adriamycin were toxic. Hence, anthracycline antineoplastic activity may be related to production of large, bulky lesions in DNA, while toxicity may correlate with toxicity measured in a simple E. coli DNA repair mutant test system.
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PMID:Interactions of the UVRABC endonuclease in vivo and in vitro with DNA damage produced by antineoplastic anthracyclines. 637 70

The unc operon of Escherichia coli was split into two fragments by the restriction endonuclease HindIII. The operator-proximal portion was cloned into plasmid pACYC184, forming plasmid pAN51, which included the genes uncB, uncE, and uncA. When plasmid pAN51 was used as template in an in vitro transcription/translation system, the alpha subunit (from the uncA gene) and delta subunit of the F(1) adenosine triphosphatase (ATPase) were formed. In addition, three polypeptides of molecular weights 18,000, 17,000, and 14,000 were formed, and the significance of these polypeptides is discussed. The operator-distal portion of the unc operon was also cloned into plasmid pACYC184, forming plasmid pAN36, which included the uncD and uncC genes. When this plasmid was used as template in an in vitro transcription/translation system, the beta subunit (from the uncD gene) and the epsilon subunit (from the uncC gene) of the F(1) ATPase were formed. A polypeptide of a molecular weight similar to the epsilon subunit but of different net charge was also formed. Plasmid pAN45, carrying the complete unc operon, was isolated after digestion of a mixture of plasmids pAN51 and pAN36 with the restriction endonuclease HindIII and then religation with T4 deoxyribonucleic acid ligase. It was concluded that a HindIII restriction site occurred within the newly described uncG gene, which was shown, by complementation studies with Mu-induced mutants, to be located between the uncA and uncD genes to give the gene order uncBEAGDC. The uncG gene appears to code for the gamma subunit of the F(1) ATPase.
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PMID:Subunits of the adenosine triphosphatase complex translated in vitro from the Escherichia coli unc operon. 644 44

This paper presents a versatile and efficient procedure for the construction of oligodeoxyribonucleotide directed site-specific mutations in DNA fragments cloned into M13 derived vectors. As an example, production of a transition mutation in a clone of the yeast MATa1 gene is described. The oligonucleotide is hybridized to the template DNA and covalently closed closed double stranded molecules are generated by extension of the oligonucleotide primer with E. coli DNA polymerase (large fragment) and ligation with T4 DNA ligase. The resulting double stranded closed circular DNA (CC-DNA) is separated from unligated and incompletely extended molecules by alkaline sucrose gradient centrifugation. This purification is essential for production of mutants at high efficiency. Competent E. coli JM101 cells are transformed with the CC-DNA fraction and single stranded DNA is isolated from individual plaques. The recombinants are screened for mutant molecules by 1) restriction endonuclease screening for the loss of the Hinf I site in the target region, and 2) by dot blot hybridization using the mutagenic oligonucleotide as probe. Double stranded DNA is isolated from the sequencing. Efficiency of mutant production is in the range of 10-45% and no precautions to prevent mismatch repair are required.
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PMID:Oligonucleotide-directed mutagenesis using M13-derived vectors: an efficient and general procedure for the production of point mutations in any fragment of DNA. 675 64

A composite plasmid pLS253 was constructed from pLS103 [carrying the Bacillus subtilis leucine genes on B. subtilis (natto) plasmid pLS28] and pHV14 [a recombinant plasmid composed of pBR322 and the staphylococcal R-plasmid pC194] employing BamHI endonuclease, T4 DNA ligase, and B. subtilis transformation. All the Leu+ Cmr transformants tested harbored not only pLS253 but also two smaller plasmids designated as pLS251 and pLS252. pLS253 DNA, when purified on an agarose gel, retained both Leu+ and Cmr transforming activities; however, in all the Leu+ Cmr transformants, the two smaller plasmids reappeared. pLS251 and pLS252 exhibited Leu+- or Cm4-transforming activity, respectively, and must have been derived from the pLS253 parent by an intramolecular recombination event, since the sum of the pLS251 and pLS252 DNAs represent the entire pLS253 genome. The recombination occurred between specific sites on the B. subtilis (natto) and Staphylococcus aureus plasmids. When the composite plasmid, pLS254, was constructed by BamHI cleavage of pLS251 and pLS252 followed by ligation, Leu+ Cmr transformants segregated two smaller plasmids which were indistinguishable from the original plasmids pLS103 and pHV14, respectively. They must have been derived from pLS254 through a reversal of the original recombination event. No intermolecular recombination between pLS251 and pLS252 DNA was detected. The recombination process was independent of recE function of the host cells, and its mechanism is discussed.
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PMID:A site-specific recE4-independent intramolecular recombination between Bacillus subtilis and Staphylococcus aureus DNAs in hybrid plasmids. 678 75

The ability of HeLa DNA polymerases to carry out DNA synthesis from incisions made by various endodeoxyribonucleases which recognize or form baseless sites in DNA was examined. DNA polymerase beta carried out limited strand displacement synthesis from 3'-hydroxyl nucleotide termini made by HeLa apurinic/apyrimidinic (AP) endonuclease II at the 5'-side of apurinic sites. Escherichia coli endonuclease III incises at the 3'-side of apurinic sites to produce nicks with 3'-deoxyribose termini which did not efficiently support DNA synthesis with beta-polymerase. However, these nicks could be activated to support limited DNA synthesis by HeLa AP endonuclease II, an enzyme which removes the baseless sugar phosphate from the 3'-termini, thus creating a one-nucleotide gap. With dGTP as the only nucleoside triphosphate present, the beta-polymerase catalyzed one-nucleotide DNA repair synthesis from those gaps which lacked dGMP. In contrast, HeLa DNA polymerase alpha was unreactive with all of the above incised DNA substrates. Larger patches of DNA synthesis were produced by nick translation from one-nucleotide gaps with HeLa DNA polymerase beta and HeLa DNase V. Moreover, incisions made by E. coli endonuclease III were activated to support DNA synthesis by the DNase V which removed the 3'-deoxyribose termini. HeLa DNase V also stimulated both the rate and extent of DNA synthesis by DNA polymerase beta from AP endonuclease II incisions. In this case the baseless sugar phosphate was removed from the 5'-termini, and nick translational synthesis occurred. Complete DNA excision repair of pyrimidine dimers was achieved with the beta-polymerase, DNase V, and DNA ligase from incisions made in UV-irradiated DNA by T4 UV endonuclease and HeLa AP endonuclease II. Such incisions produce a one-nucleotide gap containing 3'-hydroxyl nucleotide and 5'-thymine: thymidylate cyclobutane dimer termini. DNase V removes pyrimidine dimers primarily as a dinucleotide and then promotes nick translational DNA synthesis.
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PMID:Excision repair and DNA synthesis with a combination of HeLa DNA polymerase beta and DNase V. 684 90

A procedure has been developed for the rapid purification of the enzyme T4 DNA ligase. The procedure involves the induction at 42 degrees C of a lambda lysogen containing the gene for T4 DNA ligase (Murray, N.E., Bruce, S.A., and Murray, K. (1979) J. Mol. Biol. 132, 493-504), followed by purification of the ligase activity by phosphocellulose and hydroxylapatite chromatography. This results in the purification of large amounts of ligase with very high specific activity. The enzyme is free of contaminating exo- and endonuclease activities and active in the ligation of DNA fragments possessing cohesive or blunt-end termini.
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PMID:The rapid purification of T4 DNA ligase from a lambda T4 lig lysogen. 698 6

The yeast strain cdc9 which possesses a temperature-sensitive DNA ligase, was used to estimate DNA repair after mutagen exposure. Following low UV fluences, single-strand breaks in DNA were detected after an incubation at the restrictive temperature but were absent at the permissive temperature. These DNA breaks were shown to be equal to the number of pyrimidine dimers induced in DNA as measured by the presence of UV-endonuclease sensitive sites. Similarly, after exposure to the chemical mutagen 4-chloromethyl-biphenyl (4CMB) single-strand breaks accumulated at the restrictive temperature. Hence the technique described should be applicable for the estimation of the early steps of repair of a wide range of different types of DNA damage induced in yeast by exposure to either physical or chemical mutagens.
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PMID:The use of a yeast strain with a temperature-sensitive DNA ligase to estimate DNA repair after exposure to mutagens. 704 57

A DNA ligase has been purified from a subnuclear soluble replication complex isolated from adenovirus type 2-infected human KB cells. DNA ligase activity could not be demonstrated using an exogenous template until the complex was dissociated, suggesting that the ligase activity may be a component of the complex. The purified enzyme was free of endonuclease, exonuclease, 5'-nucleotidase, and phosphatase activities, and had a molecular weight of 105 000, as estimated by sedimentation in a glycerol gradient. The ligase requires ATP and a divalent cation for activity. The optimum of the reaction is at pH 7.8 in 50--100 mM Tris-HCl buffer and 10--20 mM MgCl2. Monovalent salts greatly stimulate ligase activity and the optimum was found at 150 mM. The reaction is very sensitive to high temperature; maximum activity was observed at 25--30 degrees C. ATP is the sole required cofactor and NAD, dATP and GTP could not replace the requirement for ATP. The Km for ATP is 60 microM. The Km for DNA is 250 microgram/ml or 1.6 nmol of terminal phosphate/ml and thus the enzyme shows relatively weak affinity for exogenous DNA. The maximum conversion of 32P into a phosphatase-resistant form is approximately 1.3% of the total, whereas T4 ligase, under the same conditions, can convert more than 25% of phosphate into a resistant form.
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PMID:Purification and properties of a DNA ligase from a soluble DNA replication complex. 735 2

The aim of this paper was to test the possibility to ligate and hydrolyse DNA sequences containing thiomodified ends and bonds. T4 DNA ligase was shown to ligate DNA fragments regardless of whether it contains phosphorylated or thiophosphorylated 5'-end. But the cleavage of an internally thiomodified phosphodiester bond was found to be totally inhibited when using the non-palindromic restrictase Bbs I. The special properties of this restriction endonuclease should allow the development of an oriented cloning strategy when combined with T4 ligase and a thiophosphorylation of DNA fragments.
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PMID:The accessibility of thiophosphorylated groups in DNA fragments to the enzymatic activity of ligases and restriction endonuclease Bbs I. 758 Sep 99


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