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Query: EC:6.5.1.2 (DNA ligase)
 2,749 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Plasmid lambdadv1, which is in a dimeric form, was converted to a linear monomer duplex by the action of EcoRI restriction endonuclease that incises at a unique site in this plasmid genome. The resulting products were then joined by Escherichia coli DNA ligase to produce molecules with various oligomeric forms, and from these monomeric, dimeric, or trimeric circular molecules were purified. By transformation of cells with these DNAs, clones were obtained that carried lambdadv1 in a monomeric or dimeric form. The former type of clones have not been generated in vivo, except for one in a different host strain, and carriers of timeric or tetrameric lambdadv1's have not been obtained so far. It was observed that a considerable fraction of these oligomeric circular DNAs were converted to lower oligomers (e.g., from trimer to dimer) during transformation. The characteristics of the monomeric lambdadv1 carriers obtained were compared with those of dimeric lambdadv1 carriers. The stabilities of the plasmids of the two forms were the same. However, the monomeric plasmid carriers were less tolerant to lambdavir phage infection and perpetuated about 30% less plasmid genomes in monomer units. Furthermore, dimeric plasmid carriers appeared spontaneously and accumulated in cultures of the monomeric lambdadv1 carriers.
J Virol 1975 Sep
PMID:In vitro construction of different oligomeric forms of lambdadv DNA and studies of their transforming activities. 109 30

Highly purified DNA ligase from T4 infected E. coli displays an RNA nicking activity which cleaves endonucleolytically the RNA of ribo-desoxy-and ribo-ribo type doublestranded structures to oligonucleotides with 5'phosphoryl-and 3'hydroxy termini. In the presence of ATP the generated nicks are repaired by the ligase except at the ends of the doublestranded regions where some short oligonucleotides are released before ligation can occur. As judged from its behaviour during the various purification steps and from some of its properties, the nicking activity seems to be different from known nicking enzymes.
Nucleic Acids Res 1975 Sep
PMID:RNA nicking activity associated with DNA ligase of T4 infected E. coli: properties and influence on in vitro reactions of ligase. 110 Dec 28

DNA from lambdagt-lambdaB bacteriophage was cleaved with EcoRI endonuclease and fragments from EcoRI-digested E. coli DNA were inserted. This DNA was used to infect E. coli, and phages containing the gene for DNA ligase were isolated by genetic selection. Two different hybrids were found with the same E. coli segment inserted in opposite orientations. Both hybrids produced similar levels of ligase as measured in crude extracts of infected cells.
Proc Natl Acad Sci U S A 1975 Sep
PMID:In vitro construction of bacteriophage lambda carrying segments of the Escherichia coli chromosome: selection of hybrids containing the gene for DNA ligase. 110 46

We have investigated whether J kappa recombination signal sequence (RS) binding protein (RBP-J kappa) has any partial catalytic activities involved in the VDJ recombination reaction, such as cleavage, ligation, and bending of DNA. Murine RBP-J kappa protein purified by J kappa-RS affinity chromatography did not show DNA cleavage activities but contained a strong DNA ligase activity. To obtain a large amount of purified RBP-J kappa protein, recombinant RBP-J kappa was synthesized in Escherichia coli as a fusion protein and also in silkworm cells. Although recombinant RBP-J kappa produced in silkworm cells could bind J kappa-RS, it failed to show either ligase or DNA bending activity. Since the DNA affinity-purified RBP-J kappa has the ligase activity, the RBP-J kappa protein may form a complex with a ligase in vivo. We have raised monoclonal antibodies against the RBP-J kappa fusion protein which was synthesized in E. coli and unable to bind J kappa-RS. Using the anti-RBP-J kappa monoclonal antibody we have shown that the RBP-J kappa protein is expressed ubiquitously in mammalian tissues. The ubiquitous expression of the RBP-J kappa protein is consistent with the hypothesis that the RBP-J kappa protein may have dual function [Furukawa et al. (1991) J. Biol. Chem. 266, 23334-23340].
J Biochem 1992 Sep
PMID:Biochemical and immunological characterization of the DNA binding protein (RBP-J kappa) to mouse J kappa recombination signal sequence. 142 18

The Zymomonas mobilis lig gene that encodes DNA ligase was cloned from a cosmid library and identified by genetic complementation of a conditional-lethal Escherichia coli DNA ligase mutant. Nucleotide sequence analysis of the Z. mobilis lig region indicated that the gene is 2196 bp long, encoding a protein with a deduced molecular mass of 82,089. The primary amino acid sequence of the Z. mobilis ligase is 48% identical to the E. coli enzyme. Two genes located upstream of lig were identified as tgt, encoding tRNA guanine transglycosylase and uvrB, encoding the beta subunit of excision endonuclease. Computer searches did not reveal any transcriptional terminators in the 46-bp tgt-lig intergenic region, suggesting that lig may be cotranscribed with one or more upstream genes. Weak expression of lig is explained in part by frequent use of codons that are known to be rarely used in the highly expressed glycolytic gene set.
FEMS Microbiol Lett 1992 Sep 01
PMID:Cloning and molecular characterization of the DNA ligase gene (lig) from Zymomonas mobilis. 152 62

Alteration of DNA ligase I activity is a consistent biochemical feature of Bloom's syndrome (BS) cells. DNA ligase I activity in BS cells either is reduced and abnormally thermolabile or is present in an anomalously dimeric form. To assess the role of DNA ligase function in the etiology of BS, we have cloned the DNA ligase I cDNA from normal human cells by a PCR strategy using degenerate oligonucleotide primers based on conserved regions of the Saccharomyces cerevisiae and Schizosaccharomyces pombe DNA ligase genes. Human DNA ligase I cDNAs from normal and BS cells complemented a S. cerevisiae DNA ligase mutation, and protein extracts prepared from S. cerevisiae transformants expressing normal and BS cDNA contained comparable levels of DNA ligase I activity. DNA sequencing and Northern blot analysis of DNA ligase I expression in two BS human fibroblast lines representing each of the two aberrant DNA ligase I molecular phenotypes demonstrated that this gene was unchanged in BS cells. Thus, another factor may be responsible for the observed reduction in DNA ligase I activity associated with this chromosomal breakage syndrome.
Proc Natl Acad Sci U S A 1991 Sep 01
PMID:A wild-type DNA ligase I gene is expressed in Bloom's syndrome cells. 188 2

When animals are treated with carcinogenic agents that alkylate O6-guanine residues, the incidence of tumors in specific tissues often relates inversely to the level of the DNA repair enzyme O6-methylguanine-DNA methyltransferase (MGMT) present in the tissue. Similarly, the hypersensitivity to anticancer chloroethylnitrosoureas of some human tumor cell lines is believed to result from their deficiency in MGMT. We have undertaken a comprehensive investigation of MGMT expression in a panel of nine characterized human glioma cell lines. Methyltransferase activity determined by incubating protein extracts of these glioma lines with [3H]methylated DNA ranged from undetectable in six lines (the Mer- phenotype) to greater than 0.8 pmol/mg in two lines (U-373 MG and D-392 MG). MGMT protein was undetectable in Western blots of the Mer- cell extracts probed with specific anti-MGMT monoclonal antibodies. Consistent with these results, steady-state levels of MGMT mRNA, determined by Northern blot analysis, were detectable only in the three Mer+ glioma lines (U-373 MG, D-392 MG, D-263 MG). Southern analysis of EcoRI-digested DNA probed with MGMT cDNA revealed no amplification, rearrangement or deletions of the MGMT gene in any of the glioma cell lines. This is the first report that examines MGMT expression at the biochemical, molecular and genetic levels in a particular tumor type. These studies suggest that transcriptional regulation is the basis of the Mer- phenotype in these malignant human glioma cell lines, since no gross structural or quantitative abnormalities of the MGMT gene were seen in the phenotypically Mer- lines.
Carcinogenesis 1991 Sep
PMID:Expression of O6-methylguanine-DNA methyltransferase in malignant human glioma cell lines. 189 34

Endonuclease V, a pyrimidine dimer-specific DNA repair enzyme, was chemically modified by reductive methylation, a technique that specifically methylates primary amino groups. Upon reaction of endonuclease V with [14C]formaldehyde (14CH2O) in the presence of the reducing agent sodium cyanoborohydride (Na-CNBH3), it was discovered that 0.8 methylation/endonuclease V molecule was required to reduce both the glycosylase and the phosphodiester lyase activities by 70-80%. Pyrimidine dimer-specific binding was not eradicated at a level of methylation equivalent to 0.8 CH3/endonuclease V molecule but was eradicated at higher levels of methylation. Endonuclease V that had been modified with an average of 1.6 CH3/molecule was digested with Staphylococcus aureus strain V8 protease and the peptides subsequently separated by reverse-phase high performance liquid chromatography. Radiolabel was found exclusively on the peptide including the amino terminus, as determined by the percent amino acid composition. Neither intact CH3-endonuclease V nor radiolabeled peptides were able to be sequenced by Edman degradation indicating blockage of the amino terminus by methylation. This study shows strong evidence for the unusual involvement of the alpha NH2 moiety in the chemical mechanisms of endonuclease V. A reaction mechanism that incorporates these findings is presented.
J Biol Chem 1991 Sep 15
PMID:Reductive methylation of the amino terminus of endonuclease V eradicates catalytic activities. Evidence for an essential role of the amino terminus in the chemical mechanisms of catalysis. 189 43

Drosophila melanogaster contains DNA ligases I and II. The activity of DNA ligase I is especially high during early embryonic periods, but decreases rapidly afterwards. Although the activity of DNA ligase II is low, it persists throughout all developmental stages. The specific activity of DNA ligase II is high in embryos, but the total activity per body mass was highest in pupae. To characterize the properties of DNA ligase II further and to clarify its differences from DNA ligase I, DNA ligase II was prepared from pupae of D. melanogaster. The enzyme was purified about 3200-fold by ammonium sulfate fractionation (40-70% saturation), phosphocellulose (P11) and Ultrogel column chromatography. Some of the properties have been reported previously. The isoelectric point of DNA ligase II was 6.4 while those of DNA ligase I were 4.9 and 5.8. The optimum pH of DNA ligase II was 7.8-8.1 but 8.0-8.5 for DNA ligase I. The molecular masses of DNA ligase II adducts with AMP were determined as 90 and 70 kDa. These adducts were degraded to 42 and 14.4 kDa by trypsin digestion. For preparation of monoclonal antibodies, a mouse was immunized with the purified enzyme. Two clones, 10-6 and 3-3 IgM, were obtained and purified from mouse ascites. These antibodies showed both binding and neutralizing activities toward DNA ligase II from D. melanogaster, but did not react with DNA ligase I from the same origin. These results showed clearly that DNA ligases I and II have different properties and suggest they have different roles during the developmental stages of D. melanogaster.
Eur J Biochem 1990 Sep 24
PMID:Purification and characterization of DNA ligase II from Drosophila melanogaster. 212 58

DNA break processing is compared in the Indian muntjac cell lines, SVM and DM. The initial frequencies and resealing of X-ray generated single- and double-strand breaks are similar in the two cell lines. Inhibiting the repair of UV damage leads to greater double-strand breakage in SVM than in DM, and some of these breaks are not repaired; however, repair-associated single-strand breakage and resealing are normal. Dimethylsulfate also induces excess double-strand breakage in SVM, and these breaks are irreparable. Restricted plasmids are reconstituted correctly in SVM at approximately 30% of the frequency observed in DM. Thus SVM has a reduced capacity to repair certain types of double-strand break. This defect is not due to a DNA ligase deficiency. We conclude that DNA double-strand breaks are repaired by a variety of pathways within mammalian cells and that the structure of the break or its mode of formation determines its subsequent fate.
Somat Cell Mol Genet 1990 Sep
PMID:Multiple pathways of DNA double-strand break processing in a mutant Indian muntjac cell line. 217 53


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