1
|
Archaeal DNA Polymerase-B as a DNA Template Guardian: Links between Polymerases and Base/Alternative Excision Repair Enzymes in Handling the Deaminated Bases Uracil and Hypoxanthine. ARCHAEA-AN INTERNATIONAL MICROBIOLOGICAL JOURNAL 2016; 2016:1510938. [PMID: 27721668 PMCID: PMC5045986 DOI: 10.1155/2016/1510938] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/02/2016] [Accepted: 08/01/2016] [Indexed: 02/03/2023]
Abstract
In Archaea repair of uracil and hypoxanthine, which arise by deamination of cytosine and adenine, respectively, is initiated by three enzymes: Uracil-DNA-glycosylase (UDG, which recognises uracil); Endonuclease V (EndoV, which recognises hypoxanthine); and Endonuclease Q (EndoQ), (which recognises both uracil and hypoxanthine). Two archaeal DNA polymerases, Pol-B and Pol-D, are inhibited by deaminated bases in template strands, a feature unique to this domain. Thus the three repair enzymes and the two polymerases show overlapping specificity for uracil and hypoxanthine. Here it is demonstrated that binding of Pol-D to primer-templates containing deaminated bases inhibits the activity of UDG, EndoV, and EndoQ. Similarly Pol-B almost completely turns off EndoQ, extending earlier work that demonstrated that Pol-B reduces catalysis by UDG and EndoV. Pol-B was observed to be a more potent inhibitor of the enzymes compared to Pol-D. Although Pol-D is directly inhibited by template strand uracil, the presence of Pol-B further suppresses any residual activity of Pol-D, to near-zero levels. The results are compatible with Pol-D acting as the replicative polymerase and Pol-B functioning primarily as a guardian preventing deaminated base-induced DNA mutations.
Collapse
|
2
|
Abellón-Ruiz J, Waldron KJ, Connolly BA. Archaeoglobus Fulgidus DNA Polymerase D: A Zinc-Binding Protein Inhibited by Hypoxanthine and Uracil. J Mol Biol 2016; 428:2805-13. [PMID: 27320386 PMCID: PMC4942837 DOI: 10.1016/j.jmb.2016.06.008] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2016] [Revised: 04/28/2016] [Accepted: 06/13/2016] [Indexed: 02/03/2023]
Abstract
Archaeal family-D DNA polymerases (Pol-D) comprise a small (DP1) proofreading subunit and a large (DP2) polymerase subunit. Pol-D is one of the least studied polymerase families, and this publication investigates the enzyme from Archaeoglobus fulgidus (Afu Pol-D). The C-terminal region of DP2 contains two conserved cysteine clusters, and their roles are investigated using site-directed mutagenesis. The cluster nearest the C terminus is essential for polymerase activity, and the cysteines are shown to serve as ligands for a single, critical Zn(2+) ion. The cysteines farthest from the C terminal were not required for activity, and a role for these amino acids has yet to be defined. Additionally, it is shown that Afu Pol-D activity is slowed by the template strand hypoxanthine, extending previous results that demonstrated inhibition by uracil. Hypoxanthine was a weaker inhibitor than uracil. Investigations with isolated DP2, which has a measurable polymerase activity, localised the deaminated base binding site to this subunit. Uracil and hypoxanthine slowed Afu Pol-D "in trans", that is, a copied DNA strand could be inhibited by a deaminated base in the alternate strand of a replication fork. The error rate of Afu Pol-D, measured in vitro, was 0.24×10(-5), typical for a polymerase that has been proposed to carry out genome replication in the Archaea. Deleting the 3'-5' proofreading exonuclease activity reduced fidelity twofold. The results presented in this publication considerably increase our knowledge of Pol-D.
Collapse
Affiliation(s)
- Javier Abellón-Ruiz
- Institute for Cell and Molecular Biology, University of Newcastle, Newcastle upon Tyne NE2 4HH, UK
| | - Kevin J Waldron
- Institute for Cell and Molecular Biology, University of Newcastle, Newcastle upon Tyne NE2 4HH, UK
| | - Bernard A Connolly
- Institute for Cell and Molecular Biology, University of Newcastle, Newcastle upon Tyne NE2 4HH, UK.
| |
Collapse
|
3
|
Baumann T, Arndt KM, Müller KM. Directional cloning of DNA fragments using deoxyinosine-containing oligonucleotides and endonuclease V. BMC Biotechnol 2013; 13:81. [PMID: 24090222 PMCID: PMC3856533 DOI: 10.1186/1472-6750-13-81] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2013] [Accepted: 09/25/2013] [Indexed: 02/04/2023] Open
Abstract
BACKGROUND DNA fragments carrying internal recognition sites for the restriction endonucleases intended for cloning into a target plasmid pose a challenge for conventional cloning. RESULTS A method for directional insertion of DNA fragments into plasmid vectors has been developed. The target sequence is amplified from a template DNA sample by PCR using two oligonucleotides each containing a single deoxyinosine base at the third position from the 5' end. Treatment of such PCR products with endonuclease V generates 3' protruding ends suitable for ligation with vector fragments created by conventional restriction endonuclease reactions. CONCLUSIONS The developed approach generates terminal cohesive ends without the use of Type II restriction endonucleases, and is thus independent from the DNA sequence. Due to PCR amplification, minimal amounts of template DNA are required. Using the robust Taq enzyme or a proofreading Pfu DNA polymerase mutant, the method is applicable to a broad range of insert sequences. Appropriate primer design enables direct incorporation of terminal DNA sequence modifications such as tag addition, insertions, deletions and mutations into the cloning strategy. Further, the restriction sites of the target plasmid can be either retained or removed.
Collapse
Affiliation(s)
- Tobias Baumann
- Cellular and Molecular Biotechnology, Faculty of Technology, Bielefeld University, Room UHG E2-143 Universitätsstr, 25, Bielefeld 33615, Germany.
| | | | | |
Collapse
|
4
|
Richardson TT, Wu X, Keith BJ, Heslop P, Jones AC, Connolly BA. Unwinding of primer-templates by archaeal family-B DNA polymerases in response to template-strand uracil. Nucleic Acids Res 2013; 41:2466-78. [PMID: 23303790 PMCID: PMC3575838 DOI: 10.1093/nar/gks1364] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Archaeal family-B DNA polymerases bind tightly to deaminated bases and stall replication on encountering uracil in template strands, four bases ahead of the primer-template junction. Should the polymerase progress further towards the uracil, for example, to position uracil only two bases in front of the junction, 3′–5′ proof-reading exonuclease activity becomes stimulated, trimming the primer and re-setting uracil to the +4 position. Uracil sensing prevents copying of the deaminated base and permanent mutation in 50% of the progeny. This publication uses both steady-state and time-resolved 2-aminopurine fluorescence to show pronounced unwinding of primer-templates with Pyrococcus furiosus (Pfu) polymerase–DNA complexes containing uracil at +2; much less strand separation is seen with uracil at +4. DNA unwinding has long been recognized as necessary for proof-reading exonuclease activity. The roles of M247 and Y261, amino acids suggested by structural studies to play a role in primer-template unwinding, have been probed. M247 appears to be unimportant, but 2-aminopurine fluorescence measurements show that Y261 plays a role in primer-template strand separation. Y261 is also required for full exonuclease activity and contributes to the fidelity of the polymerase.
Collapse
Affiliation(s)
- Tomas T Richardson
- Institute of Cell and Molecular Biosciences (ICaMB), The University of Newcastle, Newcastle upon Tyne NE2 4HH, UK
| | | | | | | | | | | |
Collapse
|
5
|
Gouge J, Ralec C, Henneke G, Delarue M. Molecular recognition of canonical and deaminated bases by P. abyssi family B DNA polymerase. J Mol Biol 2012; 423:315-36. [PMID: 22902479 DOI: 10.1016/j.jmb.2012.07.025] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2012] [Revised: 07/27/2012] [Accepted: 07/30/2012] [Indexed: 10/28/2022]
Abstract
Euryarchaeal polymerase B can recognize deaminated bases on the template strand, effectively stalling the replication fork 4nt downstream the modified base. Using Pyrococcus abyssi DNA B family polymerase (PabPolB), we investigated the discrimination between deaminated and natural nucleotide(s) by primer extension assays, electrophoretic mobility shift assays, and X-ray crystallography. Structures of complexes between the protein and DNA duplexes with either a dU or a dH in position +4 were solved at 2.3Å and 2.9Å resolution, respectively. The PabPolB is found in the editing mode. A new metal binding site has been uncovered below the base-checking cavity where the +4 base is flipped out; it is fully hydrated in an octahedral fashion and helps guide the strongly kinked template strand. Four other crystal structures with each of the canonical bases were also solved in the editing mode, and the presence of three nucleotides in the exonuclease site caused a shift in the coordination state of its metal A from octahedral to tetrahedral. Surprisingly, we find that all canonical bases also enter the base-checking pocket with very small differences in the binding geometry and in the calculated binding free energy compared to deaminated ones. To explain how this can lead to stalling of the replication fork, the full catalytic pathway and its branches must be taken into account, during which the base is checked several times. Our results strongly suggest a switch from elongation to editing modes right after nucleotide insertion when the modified base is at position +5.
Collapse
Affiliation(s)
- Jérôme Gouge
- Unité de Dynamique Structurale des Macromolécules, UMR 3528 du CNRS, Institut Pasteur, 25 rue du Dr Roux, 75015 Paris, France
| | | | | | | |
Collapse
|
6
|
Liu XP, Liu JH. Characterization of family IV UDG from Aeropyrum pernix and its application in hot-start PCR by family B DNA polymerase. PLoS One 2011; 6:e27248. [PMID: 22087273 PMCID: PMC3210769 DOI: 10.1371/journal.pone.0027248] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2011] [Accepted: 10/12/2011] [Indexed: 11/19/2022] Open
Abstract
Recombinant uracil-DNA glycosylase (UDG) from Aeropyrum pernix (A. pernix) was expressed in E. coli. The biochemical characteristics of A. pernix UDG (ApeUDG) were studied using oligonucleotides carrying a deoxyuracil (dU) base. The optimal temperature range and pH value for dU removal by ApeUDG were 55-65°C and pH 9.0, respectively. The removal of dU was inhibited by the divalent ions of Zn, Cu, Co, Ni, and Mn, as well as a high concentration of NaCl. The opposite base in the complementary strand affected the dU removal by ApeUDG as follows: U/C≈U/G>U/T≈U/AP≈U/->U/U≈U/I>U/A. The phosphorothioate around dU strongly inhibited dU removal by ApeUDG. Based on the above biochemical characteristics and the conservation of amino acid residues, ApeUDG was determined to belong to the IV UDG family. ApeUDG increased the yield of PCR by Pfu DNA polymerase via the removal of dU in amplified DNA. Using the dU-carrying oligonucleotide as an inhibitor and ApeUDG as an activator of Pfu DNA polymerase, the yield of undesired DNA fragments, such as primer-dimer, was significantly decreased, and the yield of the PCR target fragment was increased. This strategy, which aims to amplify the target gene with high specificity and yield, can be applied to all family B DNA polymerases.
Collapse
Affiliation(s)
- Xi-Peng Liu
- State Key Laboratory of Microbial Metabolism, School of Life Sciences & Biotechnology, Shanghai Jiao Tong University, Shanghai, China
| | - Jian-Hua Liu
- State Key Laboratory of Microbial Metabolism, School of Life Sciences & Biotechnology, Shanghai Jiao Tong University, Shanghai, China
| |
Collapse
|
7
|
Abstract
Evolution balances DNA replication speed and accuracy to optimize replicative fitness and genetic stability. There is no selective pressure to improve DNA replication fidelity beyond the background mutation rate from other sources, such as DNA damage. However, DNA polymerases remain amenable to amino acid substitutions that lower intrinsic error rates. Here, we review these 'antimutagenic' changes in DNA polymerases and discuss what they reveal about mechanisms of replication fidelity. Pioneering studies with bacteriophage T4 DNA polymerase (T4 Pol) established the paradigm that antimutator amino acid substitutions reduce replication errors by increasing proofreading efficiency at the expense of polymerase processivity. The discoveries of antimutator substitutions in proofreading-deficient 'mutator' derivatives of bacterial Pols I and III and yeast Pol δ suggest there must be additional antimutagenic mechanisms. Remarkably, many of the affected amino acid positions from Pol I, Pol III, and Pol δ are similar to the original T4 Pol substitutions. The locations of antimutator substitutions within DNA polymerase structures suggest that they may increase nucleotide selectivity and/or promote dissociation of primer termini from polymerases poised for misincorporation, leading to expulsion of incorrect nucleotides. If misincorporation occurs, enhanced primer dissociation from polymerase domains may improve proofreading in cis by an intrinsic exonuclease or in trans by alternate cellular proofreading activities. Together, these studies reveal that natural selection can readily restore replication error rates to sustainable levels following an adaptive mutator phenotype.
Collapse
Affiliation(s)
- Alan J Herr
- Department of Pathology, University of Washington, Seattle, USA
| | | | | |
Collapse
|
8
|
Horváth A, Vértessy BG. A one-step method for quantitative determination of uracil in DNA by real-time PCR. Nucleic Acids Res 2010; 38:e196. [PMID: 20864450 PMCID: PMC2995087 DOI: 10.1093/nar/gkq815] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Uracil may occur in DNA due to either cytosine deamination or thymine replacing incorporation. Its quantitative characterization is important in assessing DNA damages in cells with perturbed thymidylate metabolism or within different DNA segments involved in immunoglobulin gene diversification. The archaeal DNA polymerase from Pyrococcus furiosus binds strongly to the deaminated base uracil and stalls on uracil-containing templates. Here, we present a straightforward method for quantitative assessment of uracil in DNA within specific genomic segments. We use wild-type P. furiosus polymerase in parallel with its point mutant version which lacks the uracil-binding specificity on synthetic and genomic DNA samples to quantify the uracil content in a single-step real-time PCR assay. Quantification of the PCR results is based on an approach analogous to template copy number determination in comparing different samples. Data obtained on synthetic uracil-containing templates are verified by direct isotopic measurements. The method is also tested on physiological DNA samples from Escherichia coli and mouse cell lines with perturbed thymidylate biosynthesis. The present PCR-based method is easy to use and measures the uracil content within a genomic segment defined by the primers. Using distinct sets of primers, the method allows the analysis of heterogeneity of uracil distribution within the genome.
Collapse
Affiliation(s)
- András Horváth
- Laboratory of Genome Metabolism and Repair, Department of Applied Biotechnology, Institute of Enzymology, Hungarian Academy of Sciences, Budapest University of Technology and Economics, Budapest, Hungary
| | | |
Collapse
|
9
|
Song JG, Kil EJ, Cho SS, Kim IH, Kwon ST. An amino acid residue in the middle of the fingers subdomain is involved in Neq DNA polymerase processivity: enhanced processivity of engineered Neq DNA polymerase and its PCR application. Protein Eng Des Sel 2010; 23:835-42. [DOI: 10.1093/protein/gzq059] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
|
10
|
Killelea T, Ghosh S, Tan SS, Heslop P, Firbank SJ, Kool ET, Connolly BA. Probing the interaction of archaeal DNA polymerases with deaminated bases using X-ray crystallography and non-hydrogen bonding isosteric base analogues. Biochemistry 2010; 49:5772-81. [PMID: 20527806 DOI: 10.1021/bi100421r] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
Archaeal family-B DNA polymerases stall replication on encountering the pro-mutagenic bases uracil and hypoxanthine. This publication describes an X-ray crystal structure of Thermococcus gorgonarius polymerase in complex with a DNA containing hypoxanthine in the single-stranded region of the template, two bases ahead of the primer-template junction. Full details of the specific recognition of hypoxanthine are revealed, allowing a comparison with published data that describe uracil binding. The two bases are recognized by the same pocket, in the N-terminal domain, and make very similar protein-DNA interactions. Specificity for hypoxanthine (and uracil) arises from a combination of polymerase-base hydrogen bonds and shape fit between the deaminated bases and the pocket. The structure with hypoxanthine at position 2 explains the stimulation of the polymerase 3'-5' proofreading exonuclease, observed with deaminated bases at this location. A beta-hairpin element, involved in partitioning the primer strand between the polymerase and exonuclease active sites, inserts between the two template bases at the extreme end of the double-stranded DNA. This denatures the two complementary primer bases and directs the resulting 3' single-stranded extension toward the exonuclease active site. Finally, the relative importance of hydrogen bonding and shape fit in determining selectivity for deaminated bases has been examined using nonpolar isosteres. Affinity for both 2,4-difluorobenzene and fluorobenzimidazole, non-hydrogen bonding shape mimics of uracil and hypoxanthine, respectively, is strongly diminished, suggesting polar protein-base contacts are important. However, residual interaction with 2,4-difluorobenzene is seen, confirming a role for shape recognition.
Collapse
Affiliation(s)
- Tom Killelea
- Institute of Cell and Molecular Biosciences (ICaMB), The University of Newcastle, Newcastle upon Tyne NE2 4HH, UK
| | | | | | | | | | | | | |
Collapse
|
11
|
Gaidamaviciute E, Tauraite D, Gagilas J, Lagunavicius A. Site-directed chemical modification of archaeal Thermococcus litoralis Sh1B DNA polymerase: Acquired ability to read through template-strand uracils. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2010; 1804:1385-93. [DOI: 10.1016/j.bbapap.2010.01.024] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/30/2009] [Revised: 01/20/2010] [Accepted: 01/29/2010] [Indexed: 11/27/2022]
|
12
|
Tubeleviciute A, Skirgaila R. Compartmentalized self-replication (CSR) selection of Thermococcus litoralis Sh1B DNA polymerase for diminished uracil binding. Protein Eng Des Sel 2010; 23:589-97. [PMID: 20513707 DOI: 10.1093/protein/gzq032] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The thermostable archaeal DNA polymerase Sh1B from Thermococcus litoralis has a typical uracil-binding pocket, which in nature plays an essential role in preventing the accumulation of mutations caused by cytosine deamination to uracil and subsequent G-C base pair transition to A-T during the genomic DNA replication. The uracil-binding pocket recognizes and binds uracil base in a template strand trapping the polymerase. Since DNA replication stops, the repair systems have a chance to correct the promutagenic event. Archaeal family B DNA polymerases are employed in various PCR applications. Contrary to nature, in PCR the uracil-binding property of archaeal polymerases is disadvantageous and results in decreased DNA amplification yields and lowered sensitivity. Furthermore, in diagnostics qPCR, RT-qPCR and end-point PCR are performed using dNTP mixtures, where dTTP is partially or fully replaced by dUTP. Uracil-DNA glycosylase treatment and subsequent heating of the samples is used to degrade the DNA containing uracil and prevent carryover contamination, which is the main concern in diagnostic laboratories. A thermostable archaeal DNA polymerase with the abolished uracil binding would be a highly desirable and commercially interesting product. An attempt to disable uracil binding in DNA polymerase Sh1B from T. litoralis by generating site-specific mutants did not yield satisfactory results. However, a combination of random mutagenesis of the whole polymerase gene and compartmentalized self-replication was successfully used to select variants of thermostable Sh1B polymerase capable of performing PCR with dUTP instead of dTTP.
Collapse
|
13
|
Russell HJ, Richardson TT, Emptage K, Connolly BA. The 3'-5' proofreading exonuclease of archaeal family-B DNA polymerase hinders the copying of template strand deaminated bases. Nucleic Acids Res 2010; 37:7603-11. [PMID: 19783818 PMCID: PMC2794169 DOI: 10.1093/nar/gkp800] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Archaeal family B polymerases bind tightly to the deaminated bases uracil and hypoxanthine in single-stranded DNA, stalling replication on encountering these pro-mutagenic deoxynucleosides four steps ahead of the primer-template junction. When uracil is specifically bound, the polymerase-DNA complex exists in the editing rather than the polymerization conformation, despite the duplex region of the primer-template being perfectly base-paired. In this article, the interplay between the 3'-5' proofreading exonuclease activity and binding of uracil/hypoxanthine is addressed, using the family-B DNA polymerase from Pyrococcus furiosus. When uracil/hypoxanthine is bound four bases ahead of the primer-template junction (+4 position), both the polymerase and the exonuclease are inhibited, profoundly for the polymerase activity. However, if the polymerase approaches closer to the deaminated bases, locating it at +3, +2, +1 or even 0 (paired with the extreme 3' base in the primer), the exonuclease activity is strongly stimulated. In these situations, the exonuclease activity is actually stronger than that seen with mismatched primer-templates, even though the deaminated base-containing primer-templates are correctly base-paired. The resulting exonucleolytic degradation of the primer serves to move the uracil/hypoxanthine away from the primer-template junction, restoring the stalling position to +4. Thus the 3'-5' proofreading exonuclease contributes to the inability of the polymerase to replicate beyond deaminated bases.
Collapse
Affiliation(s)
- Henry J Russell
- Institute of Cell and Molecular Biosciences (ICaMB), University of Newcastle, Newcastle upon Tyne, NE2 4HH, UK
| | | | | | | |
Collapse
|
14
|
Abstract
Archaeal family-B DNA polymerases interact specifically with uracil and hypoxanthine, stalling replication on encountering these deaminated bases in DNA template strands. The present review describes X-ray structural data which elucidate the mechanism of read-ahead recognition of uracil and suggests how this is coupled to cessation of polymerization. The possible role of read-ahead recognition of uracil/hypoxanthine in DNA repair is discussed, as is the observation that the feature appears to be limited to replicative polymerases of the archaeal domain.
Collapse
|
15
|
Unique substrate spectrum and PCR application of Nanoarchaeum equitans family B DNA polymerase. Appl Environ Microbiol 2008; 74:6563-9. [PMID: 18791030 DOI: 10.1128/aem.00624-08] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The known archaeal family B DNA polymerases are unable to participate in the PCR in the presence of uracil. Here, we report on a novel archaeal family B DNA polymerase from Nanoarchaeum equitans that can successfully utilize deaminated bases such as uracil and hypoxanthine and on its application to PCR. N. equitans family B DNA polymerase (Neq DNA polymerase) produced lambda DNA fragments up to 10 kb with an approximately 2.2-fold-lower error rate (5.53 x 10(-6)) than Taq DNA polymerase (11.98 x 10(-6)). Uniquely, Neq DNA polymerase also amplified lambda DNA fragments using dUTP (in place of dTTP) or dITP (partially replaced with dGTP). To increase PCR efficiency, Taq and Neq DNA polymerases were mixed in different ratios; a ratio of 10:1 efficiently facilitated long PCR (20 kb). In the presence of dUTP, the PCR efficiency of the enzyme mixture was two- to threefold higher than that of either Taq and Neq DNA polymerase alone. These results suggest that Neq DNA polymerase and Neq plus DNA polymerase (a mixture of Taq and Neq DNA polymerases) are useful in DNA amplification and PCR-based applications, particularly in clinical diagnoses using uracil-DNA glycosylase.
Collapse
|
16
|
Emptage K, O'Neill R, Solovyova A, Connolly BA. Interplay between DNA polymerase and proliferating cell nuclear antigen switches off base excision repair of uracil and hypoxanthine during replication in archaea. J Mol Biol 2008; 383:762-71. [PMID: 18761016 DOI: 10.1016/j.jmb.2008.08.018] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2008] [Revised: 08/06/2008] [Accepted: 08/07/2008] [Indexed: 11/30/2022]
Abstract
Archaeal family-B DNA polymerases bind tightly to uracil and hypoxanthine (the deamination products of cytosine and adenine), resulting in profound inhibition of DNA replication. Investigation of the mechanism of inhibition, using single-turnover kinetics with polymerase in excess of DNA, indicated that deoxy-NTPs were efficiently bound to the polymerase-DNA complex but very poorly incorporated into the extending chain. Addition of the processivity factor proliferating cell nuclear antigen (PCNA) resulted in increased affinity of the polymerase for all primer-templates, producing extremely tight complexes when uracil (K(d)=16 pM) or hypoxanthine (K(d)=65 pM) was present. Analytical ultracentrifugation confirmed the stability of these complexes and revealed a polymerase/PCNA/DNA stoichiometry of 1:1:1. However, PCNA had no influence on the ability of the polymerase to read through uracil and hypoxanthine, the same kinetic parameters being observed with or without the processivity factor. The specificity constants determined using single-turnover kinetics showed that uracil and hypoxanthine slowed the polymerase by factors of approximately 5000 and 3000, respectively. Uracil and hypoxanthine are removed from DNA by base excision repair, initiated by uracil-DNA glycosylase and endonuclease V, respectively. Both enzymes are profoundly inhibited by the simultaneous binding of both PCNA and polymerase to primer-templates, with polymerase alone being much less effective. Thus, when the PCNA-polymerase complex encounters uracil/hypoxanthine in DNA templates, base excision repair is switched off, protecting the complex from a repair pathway that is dangerous in the context of single-stranded DNA formed during replication.
Collapse
Affiliation(s)
- Kieran Emptage
- Institute for Cell and Molecular Biosciences, The Medical School, University of Newcastle, Framlington Place, Newcastle upon Tyne NE2 4HH, UK
| | | | | | | |
Collapse
|
17
|
Firbank SJ, Wardle J, Heslop P, Lewis RJ, Connolly BA. Uracil recognition in archaeal DNA polymerases captured by X-ray crystallography. J Mol Biol 2008; 381:529-39. [PMID: 18614176 DOI: 10.1016/j.jmb.2008.06.004] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2008] [Revised: 05/29/2008] [Accepted: 06/02/2008] [Indexed: 11/26/2022]
Abstract
Archaeal family B DNA polymerases bind tightly to template-strand uracil and stall replication on encountering the pro-mutagenic base. This article describes an X-ray crystal structure, at 2.8 A resolution, of Thermococcus gorgonarius polymerase in complex with a DNA primer-template containing uracil in the single-stranded region. The DNA backbone is distorted to position the uracil deeply within a pocket, located in the amino-terminal domain of the polymerase. Specificity arises from a combination of hydrogen bonds between the protein backbone and uracil, with the pocket shaped to prevent the stable binding of the four standard DNA bases. Strong interactions are seen with the two phosphates that flank the uracil and the structure gives clues concerning the coupling of uracil binding to the halting of replication. The importance of key amino acids, identified by the analysis of the structure and their conservation between archaeal polymerases, was confirmed by site-directed mutagenesis. The crystal structure of V93Q, a polymerase variant that no longer recognises uracil, is also reported, explaining the V93Q phenotype by the steric exclusion of uracil from the pocket.
Collapse
Affiliation(s)
- Susan J Firbank
- Institute for Cell and Molecular Biosciences, Newcastle University, Newcastle upon Tyne NE2 4HH, UK
| | | | | | | | | |
Collapse
|
18
|
Characterization of a dITPase from the hyperthermophilic archaeon Thermococcus onnurineus NA1 and its application in PCR amplification. Appl Microbiol Biotechnol 2008; 79:571-8. [PMID: 18438658 DOI: 10.1007/s00253-008-1467-5] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2007] [Revised: 03/19/2008] [Accepted: 03/23/2008] [Indexed: 10/22/2022]
Abstract
In this study, we found that deoxyinosine triphosphate (dITP) could inhibit polymerase chain reaction (PCR) amplification of various family B-type DNA polymerases, and 0.93% dITP was spontaneously generated from deoxyadenosine triphosphate during PCR amplification. Thus, it was hypothesized that the generated dITP might have negative effect on PCR amplification of family B-type DNA polymerases. To overcome the inhibitory effect of dITP during PCR amplification, a dITP pyrophosphatase (dITPase) from Thermococcus onnurineus NA1 was applied to PCR amplification. Genomic analysis of the hyperthermophilic archaeon T. onnurineus NA1 revealed the presence of a 555-bp open reading frame with 48% similarity to HAM1-like dITPase from Methanocaldococcus jannaschii DSM2661 (NP_247195). The dITPase-encoding gene was cloned and expressed in Escherichia coli. The purified protein hydrolyzed dITP, not deoxyuridine triphosphate. Addition of the purified protein to PCR reactions using DNA polymerases from T. onnurineus NA1 and Pyrococcus furiosus significantly increased product yield, overcoming the inhibitory effect of dITP. This study shows the first representation that removing dITP using a dITPase enhances the PCR amplification yield of family B-type DNA polymerase.
Collapse
|