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 in vitro model system including wild-type T4 DNA polymerase, the mutagenic nucleotide analogue 2-aminopurine deoxyribonucleoside triphosphate, and poly[d(A,C)] X oligo(dT) poly(dC) X oligo(dG) template-primers is used to measure the frequency of 2-aminopurine X cytosine base mispairs formed in the G X C----A X T mutational pathway. Incorporation and turnover of the analogue into DNA is dependent on the presence of cytosine on the template strand and is reduced significantly in the presence of dGTP. 2-Aminopurine X cytosine mispairs are observed to occur at a 2-3 order of magnitude greater frequency than adenine X cytosine mispairs. The frequency of inserting 2-aminopurine deoxyribonucleoside monophosphate in place of dGMP opposite template cytosine sites is about 3-6% when either strong or weak base-stacking partners are present on the primer strand. However, enzymatic proofreading of the mispair strongly depends on base-stacking partners. Greater than 85% of misinserted 2-aminopurine deoxynucleotides are excised whenever the mispairs are formed next to 5'-primer thymine sites. A 5-fold reduction in proofreading frequency occurs when the mispair is formed with 2-aminopurine deoxynucleoside monophosphate stacked adjacent to a 5'-primer guanine. The frequency of 2-aminopurine X cytosine base mispair formation in the G X C----A X T pathway is similar to that found previously in the A X T----G X C pathway (Watanabe, S. M., and Goodman, M.F. (1981) Proc. Natl. Acad. Sci. U.S.A. 78, 2864-2868). We propose a criterion for base selection by DNA polymerase to account for the unexpected similarity in base mispairing rates in the two transition pathways.
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PMID:On the molecular basis of transition mutations. Frequency of forming 2-aminopurine-cytosine base mispairs in the G X C----A X T mutational pathway by T4 DNA polymerase in vitro. 648 May 80

[3H]2-Aminopurine deoxyribonucleoside triphosphate and [32P]dATP were added exogenously at equimolar concentrations to washed HeLa cell nuclei both in the presence and absence of cell cytoplasm. The observed ratio of 2-aminopurine/adenine deoxyribonucleotide incorporation into DNA was about 12%, which is consistent with 2-aminopurine misinsertion frequencies measured in cell-free assays, for various DNA polymerases including alpha-polymerase from calf thymus, Escherichia coli polymerase I, and several mutant and wild type bacteriophage T4 polymerases. Based on the 12% 2-aminopurine/adenine misincorporation ratio, we propose that proofreading of replicating DNA is not occurring in HeLa nuclei, and that discrimination against 2-aminopurine incorporation is governed primarily by a 1.1 kcal/mol difference in free energy between 2-aminopurine.thymine and adenine.thymine base pairs rather than by properties attributable to either the mammalian DNA polymerase or HeLa cell nuclear replication apparatus.
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PMID:Evidence for the absence of DNA proofreading in HeLa cell nuclei. 725 86

DNA polymerase makes errors by misincorporating natural DNA bases and base analogs. Because of the wide variety of possible mismatches and the varying efficiency with which they are repaired, structural studies are necessary to understand in detail how these mispairs differ and can be distinguished from standard Watson-Crick base pairs. 2-Aminopurine (AP) is a highly mutagenic base analog. The objective of this study was to determine the geometry of the AP x C mispair in DNA at neutral pH. Although several studies have focused on the AP x C mispair in DNA, there is not as of yet consensus on its structure. At least four models have been proposed for this mispair. Through the use of NMR spectroscopy with selective 15N-labeling of exocyclic amino nitrogens on bases of interest, we are able to resolve ambiguities in previous studies. We find here that, in two different DNA sequences, the AP x C mispair at neutral and high pH is in a wobble geometry. The structure and stability of this base mispair is dependent upon the local base sequence.
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PMID:NMR study of the conformation of the 2-aminopurine:cytosine mismatch in DNA. 867 36