Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:6.5.1.2 (DNA ligase)
 2,749 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Activity of the DNA repair enzyme uracil-DNA glycosylase has been shown to increase in herpes simplex virus type 2 (HSV-2)-infected cells. When mRNA derived from either HSV-1- or HSV-2-infected HeLa S3 cells was translated in an in vitro translation system, significant uracil-DNA glycosylase activity could be detected in the lysate. This activity was specific for the removal of uracil from DNA. Lysates from in vitro translation of mRNA derived from uninfected HeLa cells did not contain measurable glycosylase activity. A cDNA library was constructed with mRNA derived from HSV-2-infected cells 10 h postinfection. Pooled isolates from this library were used in hybrid-arrest and in vitro translation reactions to isolate a uracil-DNA glycosylase-specific cDNA. In vitro translation of hybrid-selected RNA, by using this cDNA, produced glycosylase activity in the lysate. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of radiolabeled products from this translation reaction showed a protein component with a molecular weight of 39,000. This is consistent with the molecular weight determinations of the purified glycosylase enzyme derived from either uninfected or HSV-infected HeLa cells. Northern (RNA blot) analysis of HSV-derived RNA, by using the glycosylase cDNA as a probe, revealed five overlapping transcripts of 3.4, 2.8, 2.4, 1.7, and 1.0 kilobases. Southern analysis indicated that the DNA sequence encoding the HSV-specific uracil-DNA glycosylase was located between 0.065 and 0.08 map units on the prototypic arrangement of the HSV genome.
 ...
PMID:Isolation of a herpes simplex virus cDNA encoding the DNA repair enzyme uracil-DNA glycosylase. 304 Oct 25

The process by which DNA-interactive proteins locate specific sequences or target sites on cellular DNA within Escherichia coli is a poorly understood phenomenon. In this study, we present the first direct in vivo analysis of the interaction of a DNA repair enzyme, T4 endonuclease V, and its substrate, pyrimidine dimer-containing plasmid DNA, within UV-irradiated E. coli. A pyrimidine dimer represents a small target site within large domains of DNA. There are two possible paradigms by which endonuclease V could locate these small target sites: a processive mechanism in which the enzyme "scans" DNA for dimer sites or a distributive process in which dimers are located by random three-dimensional diffusion. In order to discriminate between these two possibilities in E. coli, an in vivo DNA repair assay was developed to study the kinetics of plasmid DNA repair and the dimer frequency (i.e. the number of dimer sites on a given plasmid molecule) in plasmid DNA as a function of time during repair. Our results demonstrate that the overall process of plasmid DNA repair initiated by T4 endonuclease V (expressed from a recombinant plasmid within repair-deficient E. coli) occurs by a processive mechanism. Furthermore, by reducing the temperature of the repair incubation, the endonuclease V-catalyzed incision step has been effectively decoupled from the subsequent steps including repair patch synthesis, ligation, and supercoiling. By this manipulation, it was determined that the overall processive mechanism is composed of two phases: a rapid processive endonuclease V-catalyzed incision reaction, followed by a slower processive mechanism, the ultimate product of which is the dimer-free supercoiled plasmid molecule.
 ...
PMID:Molecular analysis of plasmid DNA repair within ultraviolet-irradiated Escherichia coli. I. T4 endonuclease V-initiated excision repair. 304 27

The DNA sequence of the bacteriophage T4 denV gene which encodes the DNA repair enzyme endonuclease V was previously constructed behind the hybrid lambda promoter OLPR in a plasmid vector. The OLPR-denV sequence was subcloned in M13mp18 and used as template to construct site-specific mutations in the denV structural gene in order to investigate structure/function relationships between the primary structure of the protein and its various DNA binding and catalytic activities. The Lys-130 residue of the wild-type endonuclease V has been postulated to be associated with its apurinic endonuclease (AP-endonuclease) activity. The codon for Lys-130 was changed to His-130 or Gly-130, and each denV sequence was subcloned into a pEMBL expression vector. These plasmids were transformed into repair-deficient Escherichia coli (uvrA recA), and the following parameters were examined for cells or cell extracts: expression and accumulation of endonuclease V protein (K-130, H-130, or G-130); survival after UV irradiation; dimer-specific DNA binding; and kinetics of phosphodiester bond scission at pyrimidine dimer sites, dimer-specific N-glycosylase activity, and AP-endonuclease activity. The enzyme's intracellular accumulation was significantly decreased for G-130 and slightly decreased for H-130 despite normal levels of denV-specific mRNA for each mutant. On a molar basis, the endonuclease V gene products generally gave parallel levels of each of the catalytic and binding functions with K-130 greater than H-130 greater than G-130 much greater than control denV-.(ABSTRACT TRUNCATED AT 250 WORDS)
 ...
PMID:Site-directed mutagenesis of the T4 endonuclease V gene: role of lysine-130. 313 2

The ada gene of Escherichia coli encodes a 39-kDa protein which serves both as a transcriptional activator of the adaptive response to alkylating agents and as a DNA repair enzyme demethylating O6-methyl-guanine and phosphotriester residues. Here, the isolated Ada protein was found to be readily cleaved into two fragments of similar size by treatment with trypsin, chymotrypsin, subtilisin, or V8 protease. The fragments retained their respective methyltransferase activities. The Ada protein is, therefore, comprised of two stable active domains united by a central hinge region of about 10 amino acids. Post-translational modification of the Ada protein by methylation of a specific cysteine residue in the NH2-terminal domain is known to convert it to an efficient transcriptional activator. This residue has now been identified as Cys-69.
 ...
PMID:Functional domains and methyl acceptor sites of the Escherichia coli ada protein. 316 36

The UvrA, UvrB and UvrC proteins of E. coli are subunits of a DNA repair enzyme, the ABC exonuclease. In this paper we study the uvrC regulatory region. The uvrC structural gene is preceded by an open reading frame encoding a 24 kD protein. A uvrC promoter has been mapped within this gene. The transcription start of a second promoter located 5' of the 24 kD gene is mapped in vivo. We show that transcription from both promoters on the chromosome is not inducible by UV damage. The possible translation start codons of the UvrC and of the 24 kD protein are determined. Sequences encoding the N-terminal part of the UvrC protein overlap with sequences encoding the C-terminal part of the 24 kD protein. To examine a possible function of the 24 kD gene in repair, a 24 kD insertion mutant was created in the chromosome. The mutant however only slightly affects the UV sensitivity of the cell. Transcription of P3 alone provides sufficient UvrC protein for the normal repair of UV lesions.
 ...
PMID:Regulation of the Escherichia coli excision repair gene uvrC. Overlap between the uvrC structural gene and the region coding for a 24 kD protein. 329 76

The activity of a new nitrosourea (TCNU) based on the endogenous amino acid taurine was assessed in three human lung cancer xenografts growing in immunodeficient mice. Moderate activity (specific growth delays of 0.63 and 1.13 compared with controls) was seen in two non-small cell tumours after a single oral administration of 20 mg-1kg. This dose was curative in a small cell xenograft. By using high performance liquid chromatography it was possible to detect parent drug in the tumours as well as the plasma and tissues after oral administration of TCNU. Drug sensitivity was correlated inversely with the amount of the DNA repair enzyme 0(6)-methylguanine-DNA methyltransferase assayed from extracts of the tumour cells but not with the levels of parent drug within the tumour. This compound appears to have unique pharmacokinetic properties compared with other chloroethylnitrosoureas.
 ...
PMID:Activity of a new nitrosourea (TCNU) in human lung cancer xenografts. 339 Mar 69

ABC excision nuclease of Escherichia coli is a DNA repair enzyme that recognizes major helical distortions caused by bulky base adducts and incises on both sides of the adduct, thus removing the modified nucleotides in the form of a 12-13-base long oligomer. We tested the enzyme with substrates that contained unusual helical structures caused by single-base mismatches or one, three, or four extrahelical bases (loops). We find that the enzyme does not cut DNAs containing helical perturbations caused by these structures. However, when the mismatched or extrahelical bases are modified with 1-cyclohexyl-3-(2-morpholinoethyl) carbodiimide, a reagent specific for unpaired G and T residues, the enzyme incises at the modified nucleotides in the regular manner. In addition, we find that when mismatches and loops are located near pyrimidine dimers and (6-4) photoproducts they do not inhibit incision at the photoproducts by the excinuclease but sometimes affect the incision pattern. Our results indicate that ABC excinuclease may be a useful enzymatic reagent to probe the structural changes caused by mismatches and deletions in DNA and provide additional information on the requirements for incision by this repair enzyme.
 ...
PMID:Activities and incision patterns of ABC excinuclease on modified DNA containing single-base mismatches and extrahelical bases. 353 21

Non-specific generation of intracellular free radicals in excess of normal levels, e.g. by the acute radiation absorption event in cells, has led to a delayed and temporary inhibition of thymidine kinase. The enzyme activity reaches a minimum at 4 h even after a low-level exposure with full recovery soon thereafter. This process appears to represent a biochemical response to an initial physical event, but must be distinguished from the response of the DNA repair enzyme system. A reduction of cellular thymidine kinase activity is expected to cause a temporary reduction of DNA synthesis and may be of advantage to the cell. Such a response may be regarded as an instance of radiation hormesis in the sense that such a compensatory response to the stimulus of irradiation may confer protection against a repeated increase in free radical concentration whether by renewed radiation exposure or by metabolism in general. An improvement of the efficiency of repair or an increased level of free radical detoxification should be of benefit to both the individual cell and to the organism as a whole.
 ...
PMID:Intracellular stimulation of biochemical control mechanisms by low-dose, low-LET irradiation. 357 Aug 5

Oxidants are generated in vivo by multiple mechanisms, including stimulation of leukocytes, hyperoxia, metabolism of arachidonic acid, and the activation of various oxidases. When the biochemical defences to the oxidants are inadequate, injury of tissues results. This injury was observed in rabbits and rhesus monkeys when pulmonary inflammation was induced with phorbol esters or formylated peptide given intrabronchially. We have recently investigated metabolic changes in various cells exposed to oxidants that are generated from stimulated leukocytes, including H2O2, O2, and HOCl. The target cells used were P388D1 murine macrophage-like tumour cells, human peripheral lymphocytes, GM 1380 human fibroblasts and rabbit alveolar macrophages. The oxidants used were H2O2 and PMA stimulated PMNs or neutroplasts. Lysis could only be prevented when catalase was added within the first 30-40 min of H2O2 exposure indicating that early metabolic changes determined the fate of the cell. Within seconds after the addition of H2O2 to P388D1 cells activation of the hexose monophosphate shunt (HMPS) was observed indicative of increased glutathione cycle activity. At the same time DNA strand breaks (determined by an alkaline unwinding technique) were detected. They resulted in the activation of the DNA repair enzyme poly-ADP-ribose polymerase (pADP-RP) within minutes after the addition of H2O2. At the same time ATP and NAD (the substrate of pADP-RP) concentrations dropped and nicotinamide accumulated extracellularly. 10-15 min after oxidant exposure free intracellular Ca++ concentrations determined by Quin 2 fluorescence started to increase due to release from intracellular stores.(ABSTRACT TRUNCATED AT 250 WORDS)
 ...
PMID:Oxidant and protease injury of the lung. 369 17

The ABC excision nuclease of Escherichia coli is an ATP-dependent DNA repair enzyme composed of three protein subunits, UvrA, UvrB and UvrC. The DNA sequences of all three genes have been reported. UvrA, the component that binds directly to the DNA, and UvrB, which attaches itself to the UvrA-DNA complex, both contain consensus sequences though to be diagnostic of ATP-binding sites, although the UvrC sequence does not. We now report that a computer analysis of the UvrA sequence has revealed an unusual series of internal duplications centering around putative metal-binding sites which may be involved in the interaction with DNA. We also find a strong evolutionary relationship to a family of prokaryotic membrane-associated active-transport proteins.
 ...
PMID:Domainal evolution of a prokaryotic DNA repair protein and its relationship to active-transport proteins. 376 95


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>