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)

DNA polymerase III holoenzyme is responsible for chromosomal DNA synthesis in Escherichia coli and seems to be a major determinant of the fidelity of replication of this organism. Among ten different subunits of the holoenzyme, the alpha subunit, encoded by the dnaE gene, has a polymerase activity, while the epsilon subunit, encoded by the dnaQ gene, is a proofreader with a 3'-5' exonuclease activity. Using poly(dA)/oligo(dT)20 as a template-primer, misincorporation of dGMP, dCMP, and dAMP by the alpha subunit and exonucleolytic editing of those mispairs by the epsilon subunit were investigated. When the polymerization reaction was performed with the alpha subunit, dCMP and dGMP but not dAMP were misincorporated. This would suggest that the polymerase might have a base-selecting function to avoid dA:dA mispairing. A subassembly of the DNA polymerase III consisting of alpha, epsilon, and theta subunits misincorporated only dGMP. This would imply that the proofreading function of the epsilon subunit may correct the dC:dA but not the dG:dA mispair. Addition of a protein encoded by the mutT gene, defects of which cause AT to CG transversions in vivo, diminished the misincorporation of dGMP onto poly(dA) template by the alpha subunit. A dGTPase activity was associated with the MutT protein. The significance of the dGTPase activity in the prevention of dG:dA mispairing is discussed.
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PMID:Molecular mechanisms of replicational fidelity in Escherichia coli. 215 94

Bacteriophage T4 encodes most of the genes whose products are required for its DNA metabolism, and host (Escherichia coli) genes can only infrequently complement mutationally inactivated T4 genes. We screened the following host mutator mutations for effects on spontaneous mutation rates in T4: mutT (destruction of aberrant dGTPs), polA, polB and polC (DNA polymerases), dnaQ (exonucleolytic proofreading), mutH, mutS, mutL and uvrD (methyl-directed DNA mismatch repair), mutM and mutY (excision repair of oxygen-damaged DNA), mutA (function unknown), and topB and osmZ (affecting DNA topology). None increased T4 spontaneous mutation rates within a resolving power of about twofold (nor did optA, which is not a mutator but overexpresses a host dGTPase). Previous screens in T4 have revealed strong mutator mutations only in the gene encoding the viral DNA polymerase and proofreading 3'-exonuclease, plus weak mutators in several polymerase accessory proteins or determinants of dNTP pool sizes. T4 maintains a spontaneous mutation rate per base pair about 30-fold greater than that of its host. Thus, the joint high fidelity of insertion by T4 DNA polymerase and proofreading by its associated 3'-exonuclease appear to determine the T4 spontaneous mutation rate, whereas the host requires numerous additional systems to achieve high replication fidelity.
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PMID:Rates of spontaneous mutation in bacteriophage T4 are independent of host fidelity determinants. 785 54

The dgt gene of Escherichia coli encodes a deoxyguanosine triphosphate triphosphohydrolase (dGTPase) that hydrolyzes dGTP to deoxyguanosine and tripolyphosphate. The enzyme is highly specific for dGTP which is hydrolyzed with a Km of 2-5 microM. Nitrocellulose filter binding assays demonstrate that, under physiological salt conditions, dGTPase binds with apparent cooperativity to single-stranded DNA with an association constant of 7.7 x 10(6) M-1. In the presence of NaCl, dGTPase binds weakly to double-stranded DNA. In the absence of NaCl, dGTPase binds both single- and double-stranded DNA with an association constant of 1 x 10(7) M-1. The dGTPase-double-stranded DNA complex, however, is readily dissociated with NaCl. Divalent cations such as Mg2+ or Mn2+ enhance, but are not required for DNA binding. The presence of dGTP or GTP does not effect the ability of dGTPase to bind DNA. dGTPase binds to oligonucleotides of length 17-35, but with lower affinities. The homopolymers poly(dT) and poly(rU) act as effective competitors of single-stranded DNA for binding to dGTPase. The bacteriophage T7 gene 1.2 protein, which specifically inhibits the enzymatic activity of dGTPase, also prevents dGTPase from binding to single-stranded DNA. dGTPase inhibits the activity of T7 DNA polymerase on a poly(dA)-oligo(dT) template. This inhibition is reversed by prior incubation of dGTPase with the T7 gene 1.2 protein.
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PMID:DNA binding properties of the deoxyguanosine triphosphate triphosphohydrolase of Escherichia coli. 839 98