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:2.7.7.7 (DNA polymerase)
17,007 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

An enconuclease activity that reacts with x-irradiated DNA is present in extracts of E. coli. By using centrifugal methods to monitor the conversion of the supercoiled, circular double-stranded DNA for phage phi-x-174 (replicative form) or PM2 to the relaxed circular form it was possible to quantitate the rate of radiation induced endonuclease-sensitive sites in the DNA. For every single-strand break induced by x-rays under aerobic irradiation conditions, there is approximately one induced site sensitive to this endonuclease activity. Under irradiation conditions (addition OF Potassium iodide) that dramatically reduce rates of single-strand breaks and "alkalilabile" lesions, the number of endonuclease-sensitive sites relative to single-strand breaks increase approximatley 4-fold. This nuclease is present in several strains of E. coli B and K12, including mutants deficient in DNA polymerase I, recombination gene products (rec mutants), ultraviolet light incision enzyme (uvr A mutant), and endonuclease II. It is suggested that this endonuclease may be involved in an excision repair process for damages incurred in DNA by ionizing radiation.
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PMID:Endonucleolytic incision of x-irradiated deoxyribonucleic acid by extracts of Escherichia coli. 109 50

Partially thiolated polycytidylic acids MPC I-III, containing 1.7%, 3.5% and 8.6% 5-mercaptocytidylate units, respectively) inhibited the DNA polymerase of Friend leukemia virus (FLV) in the endogenic reaction as well as in the presence of poly(A)-(dT)14 or poly[d(a-T)] templates; the inhibitory activities were directly related to the percent of thiolation. Various partially thiolated RNA and DNA isolates from Ehrlich ascites cells (containing one 5-mercaptopyrimidine nucleotide/50-100 nucleotide units) also inhibited the DNA polymerases of FLV in the endogenic reaction, and also in the presence of the synthetic templates. The thiolated DNA was the most active, but the thiolated tRNA also showed substantial inhibitory effects, while the thiolated ribosomal RNA was less effective. In a bacterial DNA polymerase (E. coli-K12, using denatured DNA as template), MPC I-III showed no activity. By contrast, MPC III and several partially thiolated nucleic acid isolates significantly inhibited a regenerating rat liver DNA polymerase (I) system; among those tested, the thiolated DNA from Ehrlich ascites cells showed the highest activity. Kinetic analysis of the inhibitory action of this thiolated DNA in the rat liver enzyme system, using as template the corresponding unmodified DNA, demonstrated that the thiolated DNA acts as a competitive inhibitor of the template, with a Ki/Km ratio of 0.5.
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PMID:Polynucleotides containing 5-mercapto-substituted pyrimidines: inhibition of viral DNA polymerases and the biological implication. 110 89

The repair of single-strand breaks which arise in DNA during the uvr gene-dependent excision-repair process was examined in certain radiation-sensitive strains of Escherichia coli K12. The results suggest that the excision-repair process may be divided into two branches, one which is dependent on the presence of growth medium and also the rec+ exr+ genotype, and a second which can occur in buffer (growth medium independent) and is largely dependent on DNA polymerase I. DNA polymerase III appears to be involved in the growth-medium-dependent branch of excision repair, and also in the residual growth-medium-independent repair which occurs in polA1 cells. Chloramphenicol, dinitrophenol, and impurities present in some brands of agar all appear to inhibit the growth-medium-dependent branch of excision-repair. The similarities of the two branches of excision-repair to two known pathways for the repair of X-ray-induced DNA chain breaks are discussed.
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PMID:Dependence upon growth medium and the polA, polC, recA, recB, recC, and exrA genes of separate branches of the uvr Gene-dependent excision-repair process in Escherichia coli K12 cells. 110 61

The processing of unrepaired DNA lesions is a key to understanding and predicting the biological end points of particular DNA damages. In this study, we prepared single-stranded f1 phage (f1-K12) DNA containing dihydrothymine or beta-ureidoisobutyric acid as models for instructive or noninstructive base lesions and assessed the potential biological consequences of these lesions in vitro and in vivo. To determine the effect of the two lesions on in vitro DNA synthesis, the extent of DNA synthesis was measured by 3H-labeled nucleotide incorporation, and the newly synthesized DNA was analyzed by DNA sequencing gels. The results showed that dihydrothymine in the template was at most a weak block to in vitro DNA synthesis catalyzed by Escherichia coli DNA polymerase I Klenow fragment (Pol I) and T4 DNA polymerase. In contrast, beta-ureidoisobutyric acid constituted a very strong (probably absolute) replicative block in vitro. With Pol I, termination bands were observed either opposite or one base prior to (3' to) the putative beta-ureidoisobutyric acid depending on its position in the template. However, when DNA synthesis was catalyzed by Pol I lacking a 3'----5' exonuclease activity, termination bands were only observed opposite beta-ureidoisobutyric acid, with purine nucleotides being incorporated preferentially opposite the lesion. With T4 DNA polymerase that contains a very active 3'----5' exonuclease activity, DNA synthesis was arrested almost exclusively one base prior to (3' to) the putative beta-ureidoisobutyric acid site in the template. We also measured survival of transfecting DNA containing dihydrothymine or beta-ureidoisobutyric acid in an attempt to correlate the in vitro data with in vivo processing. In keeping with the results obtained in vitro, dihydrothymine present in transfecting f1-K12 DNA did not constitute an inactivating lesion. On the other hand, it took 0.9 beta-ureidoisobutyric acid residues per molecule to inactivate transfecting f1-K12 DNA, indicating that the lesion was an absolute replicative block in vivo. When host cells were ultraviolet-irradiated to induce the SOS response, a slight increase (about 2-fold) in survival of transfecting f1-K12 DNA containing beta-ureidoisobutyric acid was observed. The potential effects of the structures of base lesions on lesion-polymerase interactions are discussed.
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PMID:Processing of DNA base damage by DNA polymerases. Dihydrothymine and beta-ureidoisobutyric acid as models for instructive and noninstructive lesions. 198 31

Spontaneously arising histidine mutations in an Escherichia coli K12 strain deficient for DNA polymerase I were analysed at the DNA sequence level. We screened approximately 150,000 colonies and isolated 106 histidine auxotrophs. Of these, 98 were unstable hisC mutations; 12 representative mutants analysed were shown to have arisen by the excision of a single quadruplet repeat in the sequence 5'-GCTGGCTGGCTGGCTG-3'. Of the eight mutations at other sites, three hisA deletions and one hisD deletion occurred as a consequence of misalignment of tandemly repeated pentamers (hisD) or decamers (hisA). A single hisA point mutation was found to be a missense mutation. Two extended deletions, covering the his operon were not analysed. We could not identify the hisC deletion by sequencing. We conclude that polA1 is a strong mutator that induces mutations mostly of the minus frameshift and deletion type by a Streisinger-type of mispairing in repetitive DNA sequences. Finally, the possible role of a 5'-GTGG-3' sequence and its inverted or direct complements, which are found in the vicinity of all the deletions and frameshifts, is discussed.
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PMID:DNA sequence analysis of spontaneous histidine mutations in a polA1 strain of Escherichia coli K12 suggests a specific role of the GTGG sequence. 227 88

T4+ exhibits increased ultraviolet sensitivity on derivatives of Escherichia coli K12 or B lacking deoxyribonucleic acid (DNA) polymerase I. However, the sensitivity of T4v is not affected by the absence of host DNA polymerase. T4x and T4y also show increased sensitivity on DNA polymerase-deficient strains, but to a lesser extent than observed with wild-type T4. When T4x or T4y, but not T4+, are plated on a double mutant lacking both DNA polymerase and the uvrA gene product, a partial suppression of the polymerase effect is observed. Host ligase appears to be able to suppress to some extent the T4y phenotype but has no effect on wild-type T4 or other T4 mutants. T4xv incubated in E. coli B or B(s-1) in the presence of chloramphenicol (50 mug/ml) shows increased resistance over directly plated irradiated phage. Increased survival under the same conditions was not observed with T4+ or other T4 mutants. The repair of X-ray-damaged T4 was investigated by examining survival curves of T4+, T4x, T4y, T4ts43, and T4ts30. The repair processes were further defined by observing the effects of plating irradiated phage on various hosts including strains lacking DNA polymerase I or polynucleotide ligase. Two classes of effects were observed. Firstly, the x and y gene products seem to be involved in a repair system utilizing host ligase. Secondly, in the absence of host DNA polymerase, phage sensitivity is increased in an unknown manner which is enhanced by the presence of host uvrA gene product.
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PMID:Host- and phage-mediated repair of radiation damage in bacteriophage T4. 456 37

A mutant strain of E. coli, initially identified by an abnormally high frequency of recombination, has been found to be defective in the 5' --> 3' exonuclease associated with DNA polymerase I, but not in the polymerase activity. This defect is tolerated at 30 degrees , but is lethal at 43 degrees . Like other polymerase I mutants, the strain is unusually sensitive to methyl methanesulfonate and to ultraviolet irradiation; it is also unable to support the growth of phage lambda defective in general recombination, and shows a reduced rate of joining of 10S "Okazaki fragments." These results demonstrate that a functional DNA polymerase I is essential for normal growth and viability in E. coli K12.
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PMID:A conditional lethal mutant of Escherichia coli K12 defective in the 5' leads to 3' exonuclease associated with DNA polymerase I. 460 Jul 86

A mutant of Escherichia coli K12, highly resistant to ultraviolet radiation, has been isolated. Preliminary tests show that this mutant is also resistant to mitomycin C, nalidixic acid, fluorouracil and thymineless death. The mutant strain apparently repairs its damaged DNA more efficiently than wild-type E. coli K12 strains and, to do so, constitutively produces 35 times more DNA polymerase I and 12 times more endonuclease I than the wild-type strain.
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PMID:Isolation and characterization of a mutant of Escherichia coli K12 synthesizing DNA polymerase I and endonuclease I constitutively. 625 82

pMS76 is a nonconjugative, 5.54-megadalton plasmid. This plasmid is present in Escherichia coli K12 cells at about 20 copies per chromosome. In addition, the pMS76 plasmid can be mobilized by conjugative plasmids and it shares a number of other properties with the amplifiable ColE1 plasmid, including the ability to amplify copy number in the presence of chloramphenicol. However, pMS76 is compatible with ColE1-like replicons, pBR313, and with other multicopy plasmids, RSF1030 and pACYC184. Also the replication of pMS76 is rifampicin sensitive and requires DNA polymerase 1.
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PMID:pMS76, a plasmid capable of amplification by treatment with chloramphenicol. 630 Sep 47

The polA1 mutation of Escherichia coli K12 and two further mutations, resA1 and resA2, characterized in E. coli B have been shown to produce enzymatically active nonsense (amber) peptides. These enzymes can be purified to virtual homogeneity by use of the lambda polA transducing phage system. The peptides are immunologically related and react weakly but specifically with antibody to whole DNA polymerase I. In their purified form the peptides are less heat-labile than the whole enzyme or the Klenow fragment produced by proteolysis. Physiological studies indicate that all three alleles are compatible with a number of different streptomycin resistance mutations (rpsL alleles) in a variety of genetic backgrounds. There is, however, clear evidence for slight amounts of "read-through" of these mutations under these conditions. DNA sequence studies have indicated the exact nucleotides that have been mutated to produce the amber alleles. The resA1 and resA2 alleles appear to be independent isolates of the same mutation both resulting in CAG (Gln) leads to TAG (amber) at amino acid residue 298. The polA1 mutation results in TGC (Trp) leads to TAG (amber) at amino acid residue 342. The significance of these findings is discussed with reference to the structure of the whole enzyme as shown by the DNA sequence data of Joyce et al. (1982) and protein chemistry of Brown et al. (1982).
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PMID:Genetic characterization of early amber mutations in the Escherichia coli polA gene and purification of the amber peptides. 630 78


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