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)

The dnaN gene of Escherichia coli encodes the beta-subunit of DNA polymerase III and maps between the dnaA and recF genes. We demonstrated previously that dnaN and recF constitute a transcriptional unit under control of the dnaN promoters. However, the recF gene has its own promoter region located in the middle of the dnaN structural gene. In this report, we use S1 mapping of mRNAs, transcriptional and translational fusions to the galK and lacZ genes, and in vitro mutagenesis to identify and characterize three tandem transcription termination sites responsible for transcriptional polarity in the dnaN-recF operon. These sites are located in the dnaN gene, downstream from the recF promoter region. Cumulatively, they terminate about 80% of the untranslated transcripts started at the recF promoters. As expected, they do not reduce transcription coming from the dnaN promoters unless dnaN translation was prematurely disrupted by the presence of a nonsense codon. The particular arrangement of regulatory elements (promoters and terminators) in the dnaN-recF region provides an exceptional in vivo system to confirm the latent termination site model of transcriptional polarity. In addition, our results contribute to the understanding of the complex regulation of the dnaA, dnaN, and recF genes. We propose that these three genes constitute an operon and that the terminators described in this work could be used to reduce expression of the distal genes of the operon under circumstances in which the dnaN translation happens to be slowed down.
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PMID:Tandem transcription termination sites in the dnaN gene of Escherichia coli. 191 78

Current models for the mechanism of SOS mutagenesis in E. coli propose the involvement of a new or modified DNA polymerase III holoenzyme in error-prone replicative bypass of bulky DNA lesions assuming an inhibited or excluded 3'----5' proofreading exonuclease function of DNA polymerase. By promotor fusion to galK, gene fusion to lacZ and Sl analysis the in vivo regulation of dnaQ coding the proofreading subunit of DNA polymerase III holoenzyme was analyzed under conditions of induced or constitutive SOS expression. The results presented here clearly show that, at least on the level of gene expression no regulatory event seems to contribute to the assumed decrease of proofreading activity during SOS mediated error-prone bypassing of bulky lesions. On the contrary, an increase in dnaQ gene expression was observed following treatment with some SOS inducing agents which produces bulky DNA lesions.
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PMID:Regulation of the dnaQ gene of Escherichia coli in mutants expressing the SOS regulon constitutively. 224 63

The dnaN and dnaQ genes encode the beta-subunit and the epsilon-subunit of the DNA polymerase III holoenzyme. By transcriptional fusions to the galK gene, translational fusions to lacZ and comparative S1 mapping analysis, we investigated the in-vivo regulation of dnaN and dnaQ. We found that DNA damage caused by the alkylating agent methyl methanesulphonate (MMS) leads to a significant induction in dnaN and dnaQ gene expression suggesting a requirement of increased amounts of at least some DNA polymerase III holoenzyme subunits for recovery from DNA damage caused by MMS. These results are first evidences that subunits of the DNA polymerase III holoenzyme are DNA damage inducible. This MMS induction of dnaN and dnaQ gene expression is unrelated to the adaptive response. It was not observed in lexA and recA mutants which abolish the induction of the SOS response.
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PMID:Induction of dnaN and dnaQ gene expression in Escherichia coli by alkylation damage to DNA. 265 58

By promoter fusion to the galK gene and comparative S1 analysis we investigated the in vivo regulation of transcription of the dnaQ gene which encodes the epsilon-subunit of the DNA polymerase III holoenzyme carrying the 3'----5' exonucleolytic proofreading function. Induction of a mutagenic stress situation by treatment with the base analogue 2-aminopurine (2-AP) leads to an increase in dnaQ transcription. S1 mapping analysis of the two dnaQ transcripts revealed a differential promoter activation for this 2-AP induced increase in dnaQ transcription. In addition, a similar galK promoter fusion with the dnaN gene coding for the beta-subunit of the DNA polymerase III holoenzyme revealed that dnaN transcription is also 2-AP inducible as judged by galactokinase activity. This is the first evidence for the inducibility of dnaQ gene expression (and possibly of other genes of the DNA polymerase II holoenzyme) and is discussed in relation to DNA repair mechanisms.
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PMID:Expression of the Escherichia coli dnaQ (mutD) gene is inducible. 283 Apr 59

The dnaN gene of Escherichia coli encodes the beta-subunit of the DNA polymerase III holoenzyme. Previous work has established that dnaN lies immediately downstream of dnaA and that both genes may be cotranscribed from the dnaA promoters; no promoter for dnaN has been described. We investigated the in vivo regulation of transcription of the dnaN gene by transcriptional fusions to the galK gene, translational fusion to the lacZ gene and S1 mapping analysis. We found that there are at least three dnaN promoters residing entirely in the reading frame of the preceding dnaA gene, and that transcription from these promoters can occur independently of dnaA transcription which, however, extends at least up to dnaN. Furthermore, we found evidence for the inducibility of the dnaN promoters in a dam background under conditions of simultaneously reduced dnaA transcription. These results are consistent with the hypothesis that although dnaA and dnaN are organized in an operon considerable discoordinate transcription can occur, thus uncoupling dnaN and dnaA regulation, when needed.
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PMID:Discoordinate gene expression in the dnaA-dnaN operon of Escherichia coli. 285

A mutant of Escherichia coli which is more resistant to shortwave UV light than its wild-type parent strain and which can synthesise DNA polymerase I constitutively has been further analysed. It carries two mutational alleles which are located about 1.5 min apart and cotransducible by P1 with the argH locus. The two mutational alleles have been segregated and their analysis shows that one of them is responsible for UV hyper-resistance whereas the other mutation confers UV sensitivity. Recombinant plasmids carrying various sections of the polA regulatory region, linked to a galK gene, were introduced into the mutant strains. Analysis of galactokinase shows that the enzyme activity in the UV hyper-resistant mutant is increased. The results suggest that the synthesis of DNA polymerase I in E. coli is inducible.
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PMID:Inducible DNA polymerase I synthesis in a UV hyper-resistant mutant of Escherichia coli. 302 86

We have analysed the transcription levels for the convergently overlapping Escherichia coli genes for the DNA polymerase III proofreading function (dnaQ) and ribonuclease H (rnh). The two tandem dnaQ promoters are about three times more active than the single rnh promoter as shown by analysing the level of in vivo transcription using dnaQ-galK and rnh-galK fusions. In E. coli mutants constitutively expressing the pleiotropic SOS response, which includes activities that enhance DNA repair, recombination and mutagenesis, a strong reduction in rnh transcription was observed. The lexA51 recA441 double mutant which fully expresses the SOS response shows the strongest reduction in rnh transcription and the highest increase in dnaQ transcription. Nuclease S1 mapping supported the finding that a constitutive expression of SOS function leads to a strong reduction in rnh transcription.
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PMID:Reduced transcription of the rnh gene in Escherichia coli mutants expressing the SOS regulon constitutively. 303 43

The Escherichia coli dnaE and dnaQ genes encode, respectively, the alpha (polymerase) and epsilon (proofreading) subunits of DNA polymerase III. Mutations in these genes resulting in mutator or antimutator phenotypes provide important tools to understand the mechanisms by which mutations occur. One way to isolate such strains is the use of papillation assays. We used one such assay based on the reversion of the galK2 allele in cells grown on MacConkey-Gal plates. Here, we describe the identification of the galK2 mutation and its possible reversion pathways, and the characterization of 7 mutators isolated using this system. 1 mutator resided in dnaE and 6 in dnaQ. Sequencing of the galK2 allele revealed a G.C-->T.A transversion at base pair 571 that changed a glu codon (GAA) to a stop codon (TAA). The analysis of 319 revertants showed that a Gal+ phenotype can be achieved by A.T-->G.C transition, A.T-->T.A transversion and A.T-->C.G transversion. We characterized the mutator phenotypes of the newly isolated mutators by determining (i) their mutation frequencies to resistance to rifampicin and nalidixic acid in both wild-type and mutL backgrounds, (ii) their temperature sensitivity and medium dependence and (iii) their mutational specificity (by analyzing the nature of galK revertants). Based on the genomic locations of their mutations, specificity of reversion pathways and magnitude of mutator effects, the mutators can be grouped into 3 classes. These classes may represent different mutational mechanisms that include defective base insertion, defective proofreading and interference with the postreplicative mismatch-repair system.
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PMID:The Escherichia coli galK2 papillation assay: its specificity and application to seven newly isolated mutator strains. 769 54

We have previously isolated mutants of Escherichia coli that replicate their DNA with increased fidelity. These mutants have a mutation in the dnaE gene, encoding the alpha subunit of DNA polymerase III. They were isolated in a mismatch-repair-defective mutL background, in which mutations can be considered to represent uncorrected DNA replication errors. In the present study we analyze the effect of one of these alleles, dnaE911, on spontaneous mutagenesis in a mismatch-repair-proficient background. In this background, spontaneous mutations may be the sum of uncorrected replication errors and mutations resulting from other pathways. Hence, the effect of the dnaE allele may provide insights into the contribution of uncorrected DNA replication errors to spontaneous mutation. The data show that dnaE911 decreases the level of Rifr, lacI and galK mutations in this background by 1.5-2-fold. DNA sequencing of 748 forward mutants in the lacI gene reveals that this effect has a clear specificity. Transversions are decreased by approximately 3-fold, whereas transitions, frameshifts, deletions and duplications remain essentially unchanged. Among the transversions, A.T-->T.A are affected most strongly (approximately 6-fold). In addition to this effect on transversions within the lacI gene, one previously recognized A.T-->G.C base-pair substitution hotspot in the lac operator is also reduced (approximately 5-fold). The data are discussed in the light of the role of DNA replication errors in spontaneous mutation, as well as other possible explanations for the observed antimutator effects.
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PMID:Spontaneous mutation in Escherichia coli containing the dnaE911 DNA polymerase antimutator allele. 782 10