1
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Chawla M, Poater A, Oliva R, Cavallo L. Unveiling structural and energetic characterization of the emissive RNA alphabet anchored in the methylthieno[3,4- d]pyrimidine heterocycle core. Phys Chem Chem Phys 2024; 26:16358-16368. [PMID: 38805177 DOI: 10.1039/d3cp06136a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/29/2024]
Abstract
This study presents a comprehensive theoretical exploration of the fluorescent non-natural emissive nucleobases- mthA, mthG, mthC, and mthU derived from the methylthieno[3,4-d]pyrimidine heterocycle. Our calculations, aligning with experimental findings, reveal that these non-natural bases exert minimal influence on the geometry of classical Watson-Crick base pairs within an RNA duplex, maintaining H-bonding akin to natural bases. In terms of energy, the impact of the modified bases, but for mthG, is also found to be little significant. We delved into an in-depth analysis of the photophysical properties of these non-natural bases. This investigation unveiled a correlation between their absorption/emission peaks and the substantial impact of the modification on the energy levels of the highest unoccupied molecular orbitals (HOMO) and the lowest unoccupied molecular orbital (LUMO). Notably, this alteration in energy levels resulted in a significant reduction of the HOMO-LUMO gap, from approximately 5.4-5.5 eV in the natural bases, to roughly 3.9-4.7 eV in the modified bases. This shift led to a consequential change in absorption and emission spectra towards longer wavelengths, elucidating their bathochromic shift.
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Affiliation(s)
- Mohit Chawla
- King Abdullah University of Science and Technology (KAUST), Physical Sciences and Engineering Division, KAUST Catalysis Center, Thuwal 23955-6900, Saudi Arabia.
| | - Albert Poater
- Institut de Química Computacional i Catàlisi and Departament de Química, Universitat de Girona, c/Ma Aurèlia Capmany 69, Girona 17003, Catalonia, Spain
| | - Romina Oliva
- Department of Sciences and Technologies, University Parthenope of Naples, Centro Direzionale Isola C4, Naples, I-80143, Italy
| | - Luigi Cavallo
- King Abdullah University of Science and Technology (KAUST), Physical Sciences and Engineering Division, KAUST Catalysis Center, Thuwal 23955-6900, Saudi Arabia.
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2
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Jose D, Michael MM, Bentsen C, Rosenblum B, Zelaya A. A Spectroscopic Approach to Unravel the Local Conformations of a G-Quadruplex Using CD-Active Fluorescent Base Analogues. Biochemistry 2022; 61:2720-2732. [DOI: 10.1021/acs.biochem.2c00461] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Affiliation(s)
- Davis Jose
- Department of Chemistry and Physics, Monmouth University, West Long Branch, New Jersey07764, United States
| | - Miya Mary Michael
- Department of Chemistry and Physics, Monmouth University, West Long Branch, New Jersey07764, United States
| | - Christopher Bentsen
- Department of Chemistry and Physics, Monmouth University, West Long Branch, New Jersey07764, United States
| | - Brandon Rosenblum
- Department of Chemistry and Physics, Monmouth University, West Long Branch, New Jersey07764, United States
| | - Adriana Zelaya
- Department of Chemistry and Physics, Monmouth University, West Long Branch, New Jersey07764, United States
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3
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Camel BR, Jose D, Meze K, Dang A, von Hippel P. Mapping DNA conformations and interactions within the binding cleft of bacteriophage T4 single-stranded DNA binding protein (gp32) at single nucleotide resolution. Nucleic Acids Res 2021; 49:916-927. [PMID: 33367802 PMCID: PMC7826291 DOI: 10.1093/nar/gkaa1230] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2020] [Revised: 11/28/2020] [Accepted: 12/07/2020] [Indexed: 11/29/2022] Open
Abstract
In this study, we use single-stranded DNA (oligo-dT) lattices that have been position-specifically labeled with monomer or dimer 2-aminopurine (2-AP) probes to map the local interactions of the DNA bases with the nucleic acid binding cleft of gp32, the single-stranded binding (ssb) protein of bacteriophage T4. Three complementary spectroscopic approaches are used to characterize these local interactions of the probes with nearby nucleotide bases and amino acid residues at varying levels of effective protein binding cooperativity, as manipulated by changing lattice length. These include: (i) examining local quenching and enhancing effects on the fluorescence spectra of monomer 2-AP probes at each position within the cleft; (ii) using acrylamide as a dynamic-quenching additive to measure solvent access to monomer 2-AP probes at each ssDNA position; and (iii) employing circular dichroism spectra to characterize changes in exciton coupling within 2-AP dimer probes at specific ssDNA positions within the protein cleft. The results are interpreted in part by what we know about the topology of the binding cleft from crystallographic studies of the DNA binding domain of gp32 and provide additional insights into how gp32 can manipulate the ssDNA chain at various steps of DNA replication and other processes of genome expression.
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Affiliation(s)
- Benjamin R Camel
- Institute of Molecular Biology and Department of Chemistry and Biochemistry, University of Oregon, Eugene, OR 97403, USA
| | - Davis Jose
- Institute of Molecular Biology and Department of Chemistry and Biochemistry, University of Oregon, Eugene, OR 97403, USA
- Department of Chemistry and Physics, Monmouth University, West Long Branch, NJ 07764, USA
| | - Katarina Meze
- Institute of Molecular Biology and Department of Chemistry and Biochemistry, University of Oregon, Eugene, OR 97403, USA
| | - Anson Dang
- Institute of Molecular Biology and Department of Chemistry and Biochemistry, University of Oregon, Eugene, OR 97403, USA
| | - Peter H von Hippel
- Institute of Molecular Biology and Department of Chemistry and Biochemistry, University of Oregon, Eugene, OR 97403, USA
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4
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Promoter Length Affects the Initiation of T7 RNA Polymerase In Vitro: New Insights into Promoter/Polymerase Co-evolution. J Mol Evol 2019; 88:179-193. [PMID: 31863129 DOI: 10.1007/s00239-019-09922-3] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2019] [Accepted: 11/28/2019] [Indexed: 10/25/2022]
Abstract
Polymerases are integral factors of gene expression and are essential for the maintenance and transmission of genetic information. RNA polymerases (RNAPs) differ from other polymerases in that they can bind promoter sequences and initiate transcription de novo and this promoter recognition requires the presence of specific DNA binding domains in the polymerase. Bacteriophage T7 RNA polymerase (T7RNAP) is the prototype for single subunit RNA polymerases which include bacteriophage and mitochondrial RNAPs, and the structure and mechanistic aspects of transcription by T7 RNAP are well characterized. Here, we describe experiments to determine whether the prototype T7 RNAP is able to recognize and initiate at truncated promoters similar to mitochondrial promoters. Using an in vitro oligonucleotide transcriptional system, we have assayed transcription initiation activity by T7 RNAP. These assays have not only defined the limits of conventional de novo initiation on truncated promoters, but have identified novel activities of initiation of RNA synthesis. We propose that these novel activities may be vestigial activities surviving from the transition of single subunit polymerase initiation using primers to de novo initiation using promoters.
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5
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McManus JB, Emanuel PA, Murray RM, Lux MW. A method for cost-effective and rapid characterization of engineered T7-based transcription factors by cell-free protein synthesis reveals insights into the regulation of T7 RNA polymerase-driven expression. Arch Biochem Biophys 2019; 674:108045. [PMID: 31326518 DOI: 10.1016/j.abb.2019.07.010] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2019] [Revised: 06/26/2019] [Accepted: 07/13/2019] [Indexed: 12/20/2022]
Abstract
The T7 bacteriophage RNA polymerase (T7 RNAP) serves as a model for understanding RNA synthesis, as a tool for protein expression, and as an actuator for synthetic gene circuit design in bacterial cells and cell-free extract. T7 RNAP is an attractive tool for orthogonal protein expression in bacteria owing to its compact single subunit structure and orthogonal promoter specificity. Understanding the mechanisms underlying T7 RNAP regulation is important to the design of engineered T7-based transcription factors, which can be used in gene circuit design. To explore regulatory mechanisms for T7 RNAP-driven expression, we developed a rapid and cost-effective method to characterize engineered T7-based transcription factors using cell-free protein synthesis and an acoustic liquid handler. Using this method, we investigated the effects of the tetracycline operator's proximity to the T7 promoter on the regulation of T7 RNAP-driven expression. Our results reveal a mechanism for regulation that functions by interfering with the transition of T7 RNAP from initiation to elongation and validates the use of the method described here to engineer future T7-based transcription factors.
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Affiliation(s)
- John B McManus
- Army Research Laboratory - West Campus, California Institute of Technology, 1200 East California Blvd, Pasadena, CA, 91125, USA
| | - Peter A Emanuel
- US Army Combat Capabilities Development Command Chemical Biological Center, 8198 Blackhawk Rd, APG, MD, 21010, USA
| | - Richard M Murray
- California Institute of Technology, Biology and Biological Engineering, 1200 East California Blvd, Pasadena, CA, 91125, USA
| | - Matthew W Lux
- US Army Combat Capabilities Development Command Chemical Biological Center, 8198 Blackhawk Rd, APG, MD, 21010, USA.
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6
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Nucleic acid-based fluorescent methods for the determination of DNA repair enzyme activities: A review. Anal Chim Acta 2019; 1060:30-44. [DOI: 10.1016/j.aca.2018.12.055] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2018] [Revised: 12/09/2018] [Accepted: 12/18/2018] [Indexed: 12/13/2022]
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7
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Kouba T, Drncová P, Cusack S. Structural snapshots of actively transcribing influenza polymerase. Nat Struct Mol Biol 2019; 26:460-470. [PMID: 31160782 PMCID: PMC7610713 DOI: 10.1038/s41594-019-0232-z] [Citation(s) in RCA: 64] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2018] [Accepted: 04/18/2019] [Indexed: 12/15/2022]
Abstract
Influenza virus RNA-dependent RNA polymerase uses unique mechanisms to transcribe its single-stranded genomic viral RNA (vRNA) into messenger RNA. The polymerase is initially bound to a promoter comprising the partially base-paired 3' and 5' extremities of the RNA. A short, capped primer, 'cap-snatched' from a nascent host polymerase II transcript, is directed towards the polymerase active site to initiate RNA synthesis. Here we present structural snapshots, as determined by X-ray crystallography and cryo-electron microscopy, of actively initiating influenza polymerase as it transitions towards processive elongation. Unexpected conformational changes unblock the active site cavity to allow establishment of a nine-base-pair template-product RNA duplex before the strands separate into distinct exit channels. Concomitantly, as the template translocates, the promoter base pairs are broken and the template entry region is remodeled. These structures reveal details of the influenza polymerase active site that will help optimize nucleoside analogs or other compounds that directly inhibit viral RNA synthesis.
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Affiliation(s)
- Tomas Kouba
- European Molecular Biology Laboratory, Grenoble, France
| | - Petra Drncová
- European Molecular Biology Laboratory, Grenoble, France
| | - Stephen Cusack
- European Molecular Biology Laboratory, Grenoble, France.
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8
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Koh HR, Roy R, Sorokina M, Tang GQ, Nandakumar D, Patel SS, Ha T. Correlating Transcription Initiation and Conformational Changes by a Single-Subunit RNA Polymerase with Near Base-Pair Resolution. Mol Cell 2018; 70:695-706.e5. [PMID: 29775583 PMCID: PMC5983381 DOI: 10.1016/j.molcel.2018.04.018] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2017] [Revised: 02/23/2018] [Accepted: 04/19/2018] [Indexed: 11/20/2022]
Abstract
We provide a comprehensive analysis of transcription in real time by T7 RNA Polymerase (RNAP) using single-molecule fluorescence resonance energy transfer by monitoring the entire life history of transcription initiation, including stepwise RNA synthesis with near base-pair resolution, abortive cycling, and transition into elongation. Kinetically branching pathways were observed for abortive initiation with an RNAP either recycling on the same promoter or exchanging with another RNAP from solution. We detected fast and slow populations of RNAP in their transition into elongation, consistent with the efficient and delayed promoter release, respectively, observed in ensemble studies. Real-time monitoring of abortive cycling using three-probe analysis showed that the initiation events are stochastically branched into productive and failed transcription. The abortive products are generated primarily from initiation events that fail to progress to elongation, and a majority of the productive events transit to elongation without making abortive products.
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Affiliation(s)
- Hye Ran Koh
- Department of Physics and Center for the Physics of Living Cells, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA; Department of Chemistry, Chung-Ang University, Seoul 06974, Korea
| | - Rahul Roy
- Department of Physics and Center for the Physics of Living Cells, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
| | - Maria Sorokina
- Department of Physics and Center for the Physics of Living Cells, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
| | - Guo-Qing Tang
- Department of Biochemistry and Molecular Biology, Rutgers University, Robert Wood Johnson Medical School, Piscataway, NJ 08854, USA
| | - Divya Nandakumar
- Department of Biochemistry and Molecular Biology, Rutgers University, Robert Wood Johnson Medical School, Piscataway, NJ 08854, USA
| | - Smita S Patel
- Department of Biochemistry and Molecular Biology, Rutgers University, Robert Wood Johnson Medical School, Piscataway, NJ 08854, USA.
| | - Taekjip Ha
- Department of Physics and Center for the Physics of Living Cells, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA; Howard Hughes Medical Institute, Baltimore, MD 21205, USA; Departments of Biophysics and Biophysical Chemistry, Biophysics, and Biomedical Engineering, Johns Hopkins University, MD 21205, USA.
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9
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Chawla M, Poater A, Besalú-Sala P, Kalra K, Oliva R, Cavallo L. Theoretical characterization of sulfur-to-selenium substitution in an emissive RNA alphabet: impact on H-bonding potential and photophysical properties. Phys Chem Chem Phys 2018; 20:7676-7685. [PMID: 29497733 DOI: 10.1039/c7cp07656h] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
We employ density functional theory (DFT) and time-dependent DFT (TDDFT) calculations to investigate the structural, energetic and optical properties of a new computationally designed RNA alphabet, where the nucleobases, tsA, tsG, tsC, and tsU (ts-bases), have been derived by replacing sulfur with selenium in the previously reported tz-bases, based on the isothiazolo[4,3-d]pyrimidine heterocycle core. We find out that the modeled non-natural bases have minimal impact on the geometry and energetics of the classical Watson-Crick base pairs, thus potentially mimicking the natural bases in a RNA duplex in terms of H-bonding. In contrast, our calculations indicate that H-bonded base pairs involving the Hoogsteen edge of purines are destabilized as compared to their natural counterparts. We also focus on the photophysical properties of the non-natural bases and correlate their absorption/emission peaks to the strong impact of the modification on the energy of the lowest unoccupied molecular orbital. It is indeed stabilized by roughly 1.1-1.6 eV as compared to the natural analogues, resulting in a reduction of the gap between the highest occupied and the lowest unoccupied molecular orbital from 5.3-5.5 eV in the natural bases to 3.9-4.2 eV in the modified ones, with a consequent bathochromic shift in the absorption and emission spectra. Overall, our analysis clearly indicates that the newly modelled ts-bases are expected to exhibit better fluorescent properties as compared to the previously reported tz-bases, while retaining similar H-bonding properties. In addition, we show that a new RNA alphabet based on size-extended benzo-homologated ts-bases can also form stable Watson-Crick base pairs with the natural complementary nucleobases.
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Affiliation(s)
- Mohit Chawla
- King Abdullah University of Science and Technology (KAUST), Physical Sciences and Engineering Division, KAUST Catalysis Center, Thuwal 23955-6900, Saudi Arabia.
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10
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Kim HY, Li T, Jung C, Fu R, Cho DY, Park KS, Park HG. Universally applicable, quantitative PCR method utilizing fluorescent nucleobase analogs. RSC Adv 2018; 8:37391-37395. [PMID: 35557795 PMCID: PMC9089284 DOI: 10.1039/c8ra06675b] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2018] [Accepted: 10/28/2018] [Indexed: 11/21/2022] Open
Abstract
We herein describe a novel quantitative PCR (qPCR) method, which operates in both signal-off and on manners, by utilizing a unique property of fluorescent nucleobase analogs. The first, signal-off method is developed by designing the primers to contain pyrrolo-dC (PdC), one of the most common fluorescent nucleobase analogs. The specially designed single-stranded primer is extended to form double-stranded DNA during PCR and the fluorescence signal from the PdCs incorporated in the primer is accordingly reduced due to its conformation-dependent fluorescence properties. In addition, the second, signal-on method is devised by designing the primers to contain 5′-overhang sequences complementary to the PdC-incorporated DNA probes. At the initial phase, the PdC-incorporated DNA probes are hybridized to the 5′-overhang sequences of the primer, exhibiting the significantly quenched fluorescence signal, but are detached by either hydrolysis or strand displacement reaction during PCR, leading to the highly enhanced fluorescence signal. This method is more advanced than the first one since it produces signal-on fluorescence response and permits the use of a single PdC-incorporated DNA probe for the detection of multiple target nucleic acids, remarkably decreasing the assay cost. With these novel qPCR methods, we successfully quantified target nucleic acids derived from sexually transmitted disease (STD) pathogens with high accuracy. Importantly, the proposed strategies overcome the major drawbacks in the current SYBR Green and TaqMan probe-based qPCR methods such as low specificity and high assay cost. A novel quantitative PCR (qPCR) method was developed by utilizing a unique property of fluorescent nucleobase analogs (PdCs).![]()
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Affiliation(s)
- Hyo Yong Kim
- Department of Chemical and Biomolecular Engineering (BK21 Program)
- KAIST
- Daejeon 305-701
- Republic of Korea
| | - Taihua Li
- College of Biology and the Environment
- Co-Innovation Centre for Sustainable Forestry in Southern China
- Nanjing Forestry University
- Nanjing
- China
| | - Cheulhee Jung
- Department of Chemical and Biomolecular Engineering (BK21 Program)
- KAIST
- Daejeon 305-701
- Republic of Korea
| | - Rongzhan Fu
- Department of Chemical and Biomolecular Engineering (BK21 Program)
- KAIST
- Daejeon 305-701
- Republic of Korea
| | - Dae-Yeon Cho
- Labgenomics Clinical Research Institute
- Labgenomics Co. Ltd
- Yong-In
- Republic of Korea
| | - Ki Soo Park
- Department of Biological Engineering
- College of Engineering
- Konkuk University
- Seoul 05029
- Republic of Korea
| | - Hyun Gyu Park
- Department of Chemical and Biomolecular Engineering (BK21 Program)
- KAIST
- Daejeon 305-701
- Republic of Korea
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11
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Ro JJ, Go GH, Wilhelmsson LM, Kim BH. Fluorescence properties of 6-aryl-2'-deoxy-furanouridine and -pyrrolocytidine and their derivatives. Methods Appl Fluoresc 2017; 6:015004. [PMID: 28933349 DOI: 10.1088/2050-6120/aa8e19] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
2'-deoxyfuranouridine derivatives presenting various aryl groups have been synthesized through Cu(I)-catalyzed intramolecular cyclizations. Moreover, corresponding pyrrolo-dC derivatives have been synthesized and both families of compounds thoroughly characterized using UV/vis and fluorescence spectroscopy as well as time-dependent density functional theory calculations. The photophysical characterization, show that our newly synthesized derivatives of the important pyrrolo-dC family have high fluorescence quantum yields (QYs) and brightness values. Pyrrolo-dC derivative, 3a, shows an environment sensitive QY of up to >60% and brightness of almost 3000, in low polarity solvents and excitation and emission maxima between 365-381 nm and 479-510 nm, respectively, in solvents of different polarities. Two other derivatives, 3b and 3c, show high QYs and brightness values of up to 3300 that are fairly insensitive to their microenvironment. These promising photophysical features suggest future applicability as fluorescent nucleobase analogs.
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Affiliation(s)
- Jong Jin Ro
- Department of Chemistry, Division of Advanced Materials Science, Pohang University of Science and Technology, Pohang 37673, Republic of Korea
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12
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Lee CY, Park KS, Park HG. Pyrrolo-dC modified duplex DNA as a novel probe for the sensitive assay of base excision repair enzyme activity. Biosens Bioelectron 2017; 98:210-214. [DOI: 10.1016/j.bios.2017.06.052] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2017] [Revised: 06/07/2017] [Accepted: 06/25/2017] [Indexed: 01/13/2023]
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13
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A new size-expanded RNA alphabet: Computational design of benzo-homologated (xtz-) isothiazole RNA and comparisons to the x-thieno RNA. J Mol Graph Model 2017; 77:339-349. [DOI: 10.1016/j.jmgm.2017.09.011] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2017] [Revised: 09/11/2017] [Accepted: 09/12/2017] [Indexed: 11/17/2022]
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14
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Ramachandran A, Basu U, Sultana S, Nandakumar D, Patel SS. Human mitochondrial transcription factors TFAM and TFB2M work synergistically in promoter melting during transcription initiation. Nucleic Acids Res 2016; 45:861-874. [PMID: 27903899 PMCID: PMC5314767 DOI: 10.1093/nar/gkw1157] [Citation(s) in RCA: 52] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2016] [Revised: 11/02/2016] [Accepted: 11/04/2016] [Indexed: 12/26/2022] Open
Abstract
Human mitochondrial DNA is transcribed by POLRMT with the help of two initiation factors, TFAM and TFB2M. The current model postulates that the role of TFAM is to recruit POLRMT and TFB2M to melt the promoter. However, we show that TFAM has ‘post-recruitment’ roles in promoter melting and RNA synthesis, which were revealed by studying the pre-initiation steps of promoter binding, bending and melting, and abortive RNA synthesis. Our 2-aminopurine mapping studies show that the LSP (Light Strand Promoter) is melted from −4 to +1 in the open complex with all three proteins and from −4 to +3 with addition of ATP. Our equilibrium binding studies show that POLRMT forms stable complexes with TFB2M or TFAM on LSP with low-nanomolar Kd values, but these two-component complexes lack the mechanism to efficiently melt the promoter. This indicates that POLRMT needs both TFB2M and TFAM to melt the promoter. Additionally, POLRMT+TFB2M makes 2-mer abortives on LSP, but longer RNAs are observed only with TFAM. These results are explained by TFAM playing a role in promoter melting and/or stabilization of the open complex on LSP. Based on our results, we propose a refined model of transcription initiation by the human mitochondrial transcription machinery.
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Affiliation(s)
- Aparna Ramachandran
- Department of Biochemistry and Molecular Biology, Rutgers, Robert Wood Johnson Medical school, Piscataway, NJ 08854, USA
| | - Urmimala Basu
- Department of Biochemistry and Molecular Biology, Rutgers, Robert Wood Johnson Medical school, Piscataway, NJ 08854, USA.,Graduate School of Biomedical Sciences, Rutgers University, Piscataway, NJ 08854, USA
| | - Shemaila Sultana
- Department of Biochemistry and Molecular Biology, Rutgers, Robert Wood Johnson Medical school, Piscataway, NJ 08854, USA
| | - Divya Nandakumar
- Department of Biochemistry and Molecular Biology, Rutgers, Robert Wood Johnson Medical school, Piscataway, NJ 08854, USA
| | - Smita S Patel
- Department of Biochemistry and Molecular Biology, Rutgers, Robert Wood Johnson Medical school, Piscataway, NJ 08854, USA
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15
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Siegel AR, Wemmer DE. Role of the σ 54 Activator Interacting Domain in Bacterial Transcription Initiation. J Mol Biol 2016; 428:4669-4685. [PMID: 27732872 DOI: 10.1016/j.jmb.2016.10.007] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2016] [Revised: 10/03/2016] [Accepted: 10/04/2016] [Indexed: 01/05/2023]
Abstract
Bacterial sigma factors are subunits of RNA polymerase that direct the holoenzyme to specific sets of promoters in the genome and are a central element of regulating transcription. Most polymerase holoenzymes open the promoter and initiate transcription rapidly after binding. However, polymerase containing the members of the σ54 family must be acted on by a transcriptional activator before DNA opening and initiation occur. A key domain in these transcriptional activators forms a hexameric AAA+ ATPase that acts through conformational changes brought on by ATP hydrolysis. Contacts between the transcriptional activator and σ54 are primarily made through an N-terminal σ54 activator interacting domain (AID). To better understand this mechanism of bacterial transcription initiation, we characterized the σ54 AID by NMR spectroscopy and other biophysical methods and show that it is an intrinsically disordered domain in σ54 alone. We identified a minimal construct of the Aquifex aeolicus σ54 AID that consists of two predicted helices and retains native-like binding affinity for the transcriptional activator NtrC1. Using the NtrC1 ATPase domain, bound with the non-hydrolyzable ATP analog ADP-beryllium fluoride, we studied the NtrC1-σ54 AID complex using NMR spectroscopy. We show that the σ54 AID becomes structured after associating with the core loops of the transcriptional activators in their ATP state and that the primary site of the interaction is the first predicted helix. Understanding this complex, formed as the first step toward initiation, will help unravel the mechanism of σ54 bacterial transcription initiation.
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Affiliation(s)
- Alexander R Siegel
- Biophysics Graduate Group, University of California, Berkeley, CA 94720, USA
| | - David E Wemmer
- Biophysics Graduate Group, University of California, Berkeley, CA 94720, USA; Department of Chemistry, University of California, Berkeley, CA 94720, USA.
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16
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Chawla M, Poater A, Oliva R, Cavallo L. Structural and energetic characterization of the emissive RNA alphabet based on the isothiazolo[4,3-d]pyrimidine heterocycle core. Phys Chem Chem Phys 2016; 18:18045-53. [PMID: 27328414 DOI: 10.1039/c6cp03268k] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
We present theoretical characterization of fluorescent non-natural nucleobases, (tz)A, (tz)G, (tz)C, and (tz)U, derived from the isothiazolo[4,3-d]pyrimidine heterocycle. Consistent with the experimental evidence, our calculations show that the non-natural bases have minimal impact on the geometry and stability of the classical Watson-Crick base pairs, allowing them to accurately mimic natural bases in a RNA duplex, in terms of H-bonding. In contrast, our calculations indicate that H-bonded base pairs involving the Hoogsteen edge are destabilized relative to their natural counterparts. Analysis of the photophysical properties of the non-natural bases allowed us to correlate their absorption/emission peaks to the strong impact of the modification on the energy of the lowest unoccupied molecular orbital, LUMO, which is stabilized by roughly 1.0-1.2 eV relative to the natural analogues, while the highest occupied molecular orbital, HOMO, is not substantially affected. As a result, the HOMO-LUMO gap is reduced from 5.3-5.5 eV in the natural bases to 4.0-4.4 eV in the modified ones, with a consequent bathochromic shift in the absorption and emission spectra.
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Affiliation(s)
- Mohit Chawla
- King Abdullah University of Science and Technology (KAUST), Physical Sciences and Engineering Division, KAUST Catalysis Center, Thuwal 23955-6900, Saudi Arabia.
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17
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Optical absorption and emission properties of benzene-expanded Janus AT nucleobase analogues: A DFT study. Struct Chem 2016. [DOI: 10.1007/s11224-016-0743-8] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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18
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Zhang L, Zhang Z, Ren T, Tian J, Wang M. New size-expanded RNA nucleobase analogs: a detailed theoretical study. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2015; 140:407-415. [PMID: 25617981 DOI: 10.1016/j.saa.2015.01.006] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/30/2014] [Revised: 12/20/2014] [Accepted: 01/05/2015] [Indexed: 06/04/2023]
Abstract
Fluorescent nucleobase analogs have attracted much attention in recent years due to their potential applications in nucleic acids research. In this work, four new size-expanded RNA base analogs were computationally designed and their structural, electronic, and optical properties are investigated by means of DFT calculations. The results indicate that these analogs can form stable Watson-Crick base pairs with natural counterparts and they have smaller ionization potentials and HOMO-LUMO gaps than natural ones. Particularly, the electronic absorption spectra and fluorescent emission spectra are calculated. The calculated excitation maxima are greatly red-shifted compared with their parental and natural bases, allowing them to be selectively excited. In gas phase, the fluorescence from them would be expected to occur around 526, 489, 510, and 462 nm, respectively. The influences of water solution and base pairing on the relevant absorption spectra of these base analogs are also examined.
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Affiliation(s)
- Laibin Zhang
- School of Physics and Engineering, Qufu Normal University, Qufu 273165, PR China.
| | - Zhenwei Zhang
- Linyi Academy of Technology Cooperation and Application, Linyi 276001, PR China
| | - Tingqi Ren
- School of Physics and Engineering, Qufu Normal University, Qufu 273165, PR China
| | - Jianxiang Tian
- School of Physics and Engineering, Qufu Normal University, Qufu 273165, PR China.
| | - Mei Wang
- School of Physics and Engineering, Qufu Normal University, Qufu 273165, PR China
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19
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20
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Hein PP, Kolb KE, Windgassen T, Bellecourt MJ, Darst SA, Mooney RA, Landick R. RNA polymerase pausing and nascent-RNA structure formation are linked through clamp-domain movement. Nat Struct Mol Biol 2014; 21:794-802. [PMID: 25108353 PMCID: PMC4156911 DOI: 10.1038/nsmb.2867] [Citation(s) in RCA: 76] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2014] [Accepted: 07/03/2014] [Indexed: 12/11/2022]
Abstract
The rates of RNA synthesis and the folding of nascent RNA into biologically active structures are linked via pausing by RNA polymerase (RNAP). Structures that form within the RNA-exit channel can either increase pausing by interacting with RNAP or decrease pausing by preventing backtracking. Conversely, pausing is required for proper folding of some RNAs. Opening of the RNAP clamp domain has been proposed to mediate some effects of nascent-RNA structures. However, the connections among RNA structure formation and RNAP clamp movement and catalytic activity remain uncertain. Here, we assayed exit-channel structure formation in Escherichia coli RNAP with disulfide cross-links that favor closed- or open-clamp conformations and found that clamp position directly influences RNA structure formation and RNAP catalytic activity. We report that exit-channel RNA structures slow pause escape by favoring clamp opening through interactions with the flap that slow translocation.
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Affiliation(s)
- Pyae P. Hein
- Department of Biochemistry, University of Wisconsin – Madison, Madison, WI 53706, USA
| | - Kellie E. Kolb
- Department of Biochemistry, University of Wisconsin – Madison, Madison, WI 53706, USA
| | - Tricia Windgassen
- Department of Biochemistry, University of Wisconsin – Madison, Madison, WI 53706, USA
| | - Michael J. Bellecourt
- Department of Biochemistry, University of Wisconsin – Madison, Madison, WI 53706, USA
| | - Seth A. Darst
- Laboratory of Molecular Biophysics, The Rockefeller University, New York, NY 10065, USA
| | - Rachel A. Mooney
- Department of Biochemistry, University of Wisconsin – Madison, Madison, WI 53706, USA
| | - Robert Landick
- Department of Biochemistry, University of Wisconsin – Madison, Madison, WI 53706, USA
- Department of Bacteriology, University of Wisconsin – Madison, Madison, WI 53706, USA
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21
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Shrestha P, Xiao S, Dhakal S, Tan Z, Mao H. Nascent RNA transcripts facilitate the formation of G-quadruplexes. Nucleic Acids Res 2014; 42:7236-46. [PMID: 24829453 PMCID: PMC4066803 DOI: 10.1093/nar/gku416] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Recent discovery of the RNA/DNA hybrid G-quadruplexes (HQs) and their potential wide-spread occurrence in human genome during transcription have suggested a new and generic transcriptional control mechanism. The G-rich sequence in which HQ may form can coincide with that for DNA G-quadruplexes (GQs), which are well known to modulate transcriptions. Understanding the molecular interaction between HQ and GQ is, therefore, of pivotal importance to dissect the new mechanism for transcriptional regulation. Using a T7 transcription model, herein we found that GQ and HQ form in a natural sequence, (GGGGA)4, downstream of many transcription start sites. Using a newly-developed single-molecular stalled-transcription assay, we revealed that RNA transcripts helped to populate quadruplexes at the expense of duplexes. Among quadruplexes, HQ predominates GQ in population and mechanical stabilities, suggesting HQ may serve as a better mechanical block during transcription. The fact that HQ and GQ folded within tens of milliseconds in the presence of RNA transcripts provided justification for the co-transcriptional folding of these species. The catalytic role of RNA transcripts in the GQ formation was strongly suggested as the GQ folded >7 times slower without transcription. These results shed light on the possible synergistic effect of GQs and HQs on transcriptional controls.
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Affiliation(s)
- Prakash Shrestha
- Department of Chemistry and Biochemistry and School of Biomedical Sciences, Kent State University, Kent, OH 44242, USA
| | - Shan Xiao
- State Key Laboratory of Biomembrane and Membrane Biotechnology, Institute of Zoology, Chinese Academy of Sciences, Beijing 100101, P.R. China
| | - Soma Dhakal
- Department of Chemistry and Biochemistry and School of Biomedical Sciences, Kent State University, Kent, OH 44242, USA
| | - Zheng Tan
- State Key Laboratory of Biomembrane and Membrane Biotechnology, Institute of Zoology, Chinese Academy of Sciences, Beijing 100101, P.R. China
| | - Hanbin Mao
- Department of Chemistry and Biochemistry and School of Biomedical Sciences, Kent State University, Kent, OH 44242, USA
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22
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Zhang L, Zhou L, Tian J, Li X. Structural, electronic, and photophysical properties of thieno-expanded tricyclic purine analogs: a theoretical study. Phys Chem Chem Phys 2014; 16:4338-49. [DOI: 10.1039/c3cp54505a] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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23
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Zhang L, Ren T, Tian J, Yang X, Zhou L, Li X. Excited State Properties of Naphtho-Homologated xxDNA Bases and Effect of Methanol Solution, Deoxyribose, and Base Pairing. J Phys Chem B 2013; 117:3983-92. [DOI: 10.1021/jp3123242] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Laibin Zhang
- School of
Physics and Engineering, Qufu Normal University, Qufu, 273165, P. R. China
| | - Tingqi Ren
- School of
Physics and Engineering, Qufu Normal University, Qufu, 273165, P. R. China
| | - Jianxiang Tian
- School of
Physics and Engineering, Qufu Normal University, Qufu, 273165, P. R. China
| | - Xiuqin Yang
- School of
Physics and Engineering, Qufu Normal University, Qufu, 273165, P. R. China
- State Key Laboratory of Crystal Materials, Shandong University, Jinan, 250100, P. R. China
| | - Liuzhu Zhou
- School of
Physics and Engineering, Qufu Normal University, Qufu, 273165, P. R. China
| | - Xiaoming Li
- School of
Physics and Engineering, Qufu Normal University, Qufu, 273165, P. R. China
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24
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Ming X, Seela F. A Nucleobase-Discriminating Pyrrolo-dC Click Adduct Designed for DNA Fluorescence Mismatch Sensing. Chemistry 2012; 18:9590-600. [DOI: 10.1002/chem.201103385] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2011] [Revised: 04/17/2012] [Indexed: 11/10/2022]
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25
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Noé MS, Ríos AC, Tor Y. Design, synthesis, and spectroscopic properties of extended and fused pyrrolo-dC and pyrrolo-C analogs. Org Lett 2012; 14:3150-3. [PMID: 22646728 PMCID: PMC3426657 DOI: 10.1021/ol3012327] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
The syntheses of four fluorescent nucleoside analogs, related to pyrrolo-C (PyC) and pyrrolo-dC (PydC) through the conjugation or fusion of a thiophene moiety, are described. A thorough photophysical analysis of the nucleosides, in comparison to PyC, is reported.
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Affiliation(s)
- Mary S Noé
- Department of Chemistry and Biochemistry, University of California, San Diego, 9500 Gilman Drive, La Jolla, California 92093-0358, USA
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26
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Völker J, Gindikin V, Klump HH, Plum GE, Breslauer KJ. Energy landscapes of dynamic ensembles of rolling triplet repeat bulge loops: implications for DNA expansion associated with disease states. J Am Chem Soc 2012; 134:6033-44. [PMID: 22397401 PMCID: PMC3318849 DOI: 10.1021/ja3010896] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2012] [Indexed: 11/30/2022]
Abstract
DNA repeat domains can form ensembles of canonical and noncanonical states, including stable and metastable DNA secondary structures. Such sequence-induced structural diversity creates complex conformational landscapes for DNA processing pathways, including those triplet expansion events that accompany replication, recombination, and/or repair. Here we demonstrate further levels of conformational complexity within repeat domains. Specifically, we show that bulge loop structures within an extended repeat domain can form dynamic ensembles containing a distribution of loop positions, thereby yielding families of positional loop isomers, which we designate as "rollamers". Our fluorescence, absorbance, and calorimetric data are consistent with loop migration/translocation between sites within the repeat domain ("rollamerization"). We demonstrate that such "rollameric" migration of bulge loops within repeat sequences can invade and disrupt previously formed base-paired domains via an isoenthalpic, entropy-driven process. We further demonstrate that destabilizing abasic lesions alter the loop distributions so as to favor "rollamers" with the lesion positioned at the duplex/loop junction, sites where the flexibility of the abasic "universal hinge" relaxes unfavorable interactions and/or facilitates topological accommodation. Another strategic siting of an abasic site induces directed loop migration toward denaturing domains, a phenomenon that merges destabilizing domains. In the aggregate, our data reveal that dynamic ensembles within repeat domains profoundly impact the overall energetics of such DNA constructs as well as the distribution of states by which they denature/renature. These static and dynamic influences within triplet repeat domains expand the conformational space available for selection and targeting by the DNA processing machinery. We propose that such dynamic ensembles and their associated impact on DNA properties influence pathways that lead to DNA expansion.
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Affiliation(s)
- Jens Völker
- Department
of Chemistry and
Chemical Biology, Rutgers, The State University of New
Jersey, 610 Taylor Road, Piscataway, New Jersey 08854,
United States
| | - Vera Gindikin
- Department
of Chemistry and
Chemical Biology, Rutgers, The State University of New
Jersey, 610 Taylor Road, Piscataway, New Jersey 08854,
United States
| | - Horst H. Klump
- Department
of Molecular and
Cell Biology, University of Cape Town,
Private Bag, Rondebosch 7800, South Africa
| | - G. Eric Plum
- IBET Inc., 1507 Chambers
Road, Suite 301, Columbus, Ohio 43212, United States
| | - Kenneth J. Breslauer
- Department
of Chemistry and
Chemical Biology, Rutgers, The State University of New
Jersey, 610 Taylor Road, Piscataway, New Jersey 08854,
United States
- The Cancer Institute
of New Jersey, New Brunswick, New Jersey 08901, United
States
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27
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Segal M, Fischer B. Analogues of uracil nucleosides with intrinsic fluorescence (NIF-analogues): synthesis and photophysical properties. Org Biomol Chem 2012; 10:1571-80. [PMID: 22222762 DOI: 10.1039/c1ob06536j] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Uridine cannot be utilized as fluorescent probe due to its extremely low quantum yield. For improving the uracil fluorescence characteristics we extended the natural chromophore at the C5 position by coupling substituted aromatic rings directly or via an alkenyl or alkynyl linker to create fluorophores. Extension of the uracil base was achieved by treating 5-I-uridine with the appropriate boronic acid under the Suzuki coupling conditions. Analogues containing an alkynyl linker were obtained from 5-I-uridine and the suitable boronic acid in a Sonogashira coupling reaction. The uracil fluorescent analogues proposed here were designed to satisfy the following requirements: a minimal chemical modification at a position not involved in base-pairing, resulting in relatively long absorption and emission wavelengths and high quantum yield. 5-((4-Methoxy-phenyl)-trans-vinyl)-2'-deoxy-uridine, 6b, was found to be a promising fluorescent probe. Probe 6b exhibits a quantum yield that is 3000-fold larger than that of the natural chromophore (Φ 0.12), maximum emission (478 nm) which is 170 nm red shifted as compared to uridine, and a Stokes shift of 143 nm. In addition, since probe 6b adopts the anti conformation and S sugar puckering favored by B-DNA, it makes a promising nucleoside analogue to be incorporated in an oligonucleotide probe for detection of genetic material.
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Affiliation(s)
- Meirav Segal
- Department of Chemistry, Bar-Ilan University, Ramat-Gan, 52900, Israel
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28
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Park KS, Lee JY, Park HG. Mismatched pyrrolo-dC-modified duplex DNA as a novel probe for sensitive detection of silver ions. Chem Commun (Camb) 2012; 48:4549-51. [DOI: 10.1039/c2cc17148a] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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29
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Abstract
Fluorescent sensors that make use of DNA structures have become widely useful in monitoring enzymatic activities. Early studies focused primarily on enzymes that naturally use DNA or RNA as the substrate. However, recent advances in molecular design have enabled the development of nucleic acid sensors for a wider range of functions, including enzymes that do not normally bind DNA or RNA. Nucleic acid sensors present some potential advantages over classical small-molecule sensors, including water solubility and ease of synthesis. An overview of the multiple strategies under recent development is presented in this critical review, and expected future developments in microarrays, single molecule analysis, and in vivo sensing are discussed (160 references).
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Affiliation(s)
- Nan Dai
- Department of Chemistry, Stanford University, Stanford, CA 94305, USA
| | - Eric T. Kool
- Department of Chemistry, Stanford University, Stanford, CA 94305, USA
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30
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Vahia AV, Martin CT. Direct tests of the energetic basis of abortive cycling in transcription. Biochemistry 2011; 50:7015-22. [PMID: 21776950 DOI: 10.1021/bi200620q] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Although the synthesis of RNA from a DNA template is (and must be) a generally very stable process to enable transcription of kilobase transcripts, it has long been known that during initial transcription of the first 8-10 bases of RNA complexes are relatively unstable, leading to the release of short abortive RNA transcripts. A wealth of structural data in the past decade has led to specific mechanistic models elaborating an earlier "stressed intermediate" model for initial transcription. In this study, we test fundamental predictions of each of these models in the simple model enzyme T7 RNA polymerase. Nicking or gapping the nontranscribed template DNA immediately upstream of the growing hybrid yields no systematic reduction in abortive falloff, demonstrating clearly that compaction or "scrunching" of this DNA is not a source of functional instability. Similarly, transcription on DNA in which the nontemplate strand in the initially transcribed region is either mismatched or removed altogether leads to at most modest reductions in abortive falloff, indicating that expansion or "scrunching" of the bubble is not the primary driving force for abortive cycling. Finally, energetic stress derived from the observed steric clash of the growing hybrid against the N-terminal domain contributes at most mildly to abortive cycling, as the addition of steric bulk (additional RNA bases) at the upstream end of the hybrid does not lead to predicted positional shifts in observed abortive patterns. We conclude that while structural changes (scrunching) clearly occur in initial transcription, stress from these changes is not the primary force driving abortive cycling.
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Affiliation(s)
- Ankit V Vahia
- Program in Molecular & Cellular Biology, University of Massachusetts, Amherst, Massachusetts 01003, United States
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31
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Single Molecule Detection of One, Two and Multiplex Proteins Involved in DNA/RNA Transaction. Cell Mol Bioeng 2011. [DOI: 10.1007/s12195-011-0159-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
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32
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Paratkar S, Deshpande AP, Tang GQ, Patel SS. The N-terminal domain of the yeast mitochondrial RNA polymerase regulates multiple steps of transcription. J Biol Chem 2011; 286:16109-20. [PMID: 21454631 DOI: 10.1074/jbc.m111.228023] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Transcription of the yeast (Saccharomyces cerevisiae) mitochondrial (mt) genome is catalyzed by nuclear-encoded proteins that include the core RNA polymerase (RNAP) subunit Rpo41 and the transcription factor Mtf1. Rpo41 is homologous to the single-subunit bacteriophage T7/T3 RNAP. Its ∼80-kDa C-terminal domain is highly conserved among mt RNAPs, but its ∼50-kDa N-terminal domain (NTD) is less conserved and not present in T7/T3 RNAP. To understand the role of the NTD, we have biochemically characterized a series of NTD deletion mutants of Rpo41. Our studies show that NTD regulates multiple steps of transcription initiation. Interestingly, NTD functions in an autoinhibitory manner during initiation, and its partial deletion increases the efficiency of RNA synthesis. Deletion of 1-270 amino acids (DN270) reduces abortive synthesis and increases full-length to abortive RNA ratio relative to full-length (FL) Rpo41. A larger deletion of 1-380 amino acids (DN380), decreases RNA synthesis on duplex but not on premelted promoter. We show that DN380 is defective in promoter opening near the transcription start site. Most strikingly, both DN270 and DN380 catalyze highly processive RNA synthesis on the premelted promoter, and unlike the FL Rpo41, the mutants are not inhibited by Mtf1. Both mutants show weaker interactions with Mtf1, which explains many of our results, and particularly the ability of the mutants to efficiently transition from initiation to elongation. We propose that in vivo the accessory proteins that bind NTD may modulate interactions of Rpo41 with the promoter/Mtf1 to activate and allow timely release from Mtf1 for transition into elongation.
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Affiliation(s)
- Swaroopa Paratkar
- Department of Biochemistry, Robert Wood Johnson Medical School, University of Medicine and Dentistry of New Jersey, Piscataway, New Jersey 08854, USA
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33
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Dierckx A, Dinér P, El-Sagheer AH, Kumar JD, Brown T, Grøtli M, Wilhelmsson LM. Characterization of photophysical and base-mimicking properties of a novel fluorescent adenine analogue in DNA. Nucleic Acids Res 2011; 39:4513-24. [PMID: 21278417 PMCID: PMC3105426 DOI: 10.1093/nar/gkr010] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
To increase the diversity of fluorescent base analogues with improved properties, we here present the straightforward click-chemistry-based synthesis of a novel fluorescent adenine-analogue triazole adenine (AT) and its photophysical characterization inside DNA. AT shows promising properties compared to the widely used adenine analogue 2-aminopurine. Quantum yields reach >20% and >5% in single- and double-stranded DNA, respectively, and show dependence on neighbouring bases. Moreover, AT shows only a minor destabilization of DNA duplexes, comparable to 2-aminopurine, and circular dichroism investigations suggest that AT only causes minimal structural perturbations to normal B-DNA. Furthermore, we find that AT shows favourable base-pairing properties with thymine and more surprisingly also with normal adenine. In conclusion, AT shows strong potential as a new fluorescent adenine analogue for monitoring changes within its microenvironment in DNA.
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Affiliation(s)
- Anke Dierckx
- Department of Chemical and Biological Engineering/Physical Chemistry, Chalmers University of Technology, University of Gothenburg, S-41296 Gothenburg, Sweden
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34
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FRET (fluorescence resonance energy transfer) sheds light on transcription. Biochem Soc Trans 2011; 39:122-7. [DOI: 10.1042/bst0390122] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
The complex organization of the transcription machinery has been revealed mainly by biochemical and crystallographic studies. X-ray structures describe RNA polymerases and transcription complexes on an atomic level, but fail to portray their dynamic nature. The use of fluorescence techniques has made it possible to add a new layer of information to our understanding of transcription by providing details about the structural rearrangement of mobile elements and the network of interactions within transcription complexes in solution and in real-time.
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35
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Dallmann A, Dehmel L, Peters T, Mügge C, Griesinger C, Tuma J, Ernsting NP. 2-Aminopurine incorporation perturbs the dynamics and structure of DNA. Angew Chem Int Ed Engl 2010; 49:5989-92. [PMID: 20632340 DOI: 10.1002/anie.201001312] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Affiliation(s)
- André Dallmann
- Humboldt Universität zu Berlin, Institut für Chemie, 12489 Berlin, Germany
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36
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Greco NJ, Sinkeldam RW, Tor Y. An emissive C analog distinguishes between G, 8-oxoG, and T. Org Lett 2010; 11:1115-8. [PMID: 19196162 DOI: 10.1021/ol802656n] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
A minimally disruptive fluorescent dC analog provides a rapid and non-destructive method for in vitro detection of G, 8-oxoG, and T, the downstream transverse mutation product.
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Affiliation(s)
- Nicholas J Greco
- Department of Chemistry and Biochemistry, University of California, San Diego, 9500 Gilman Drive, La Jolla, California 92093-0358, USA
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37
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Dallmann A, Dehmel L, Peters T, Mügge C, Griesinger C, Tuma J, Ernsting N. Der Einbau von 2-Aminopurin beeinflusst die Dynamik und Struktur von DNA. Angew Chem Int Ed Engl 2010. [DOI: 10.1002/ange.201001312] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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38
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Ohkubo A, Sakaue T, Tsunoda H, Seio K, Sekine M. Synthesis and Hybridization Properties of Oligonucleotides Incorporating Bi- and Tricyclic Cytosine Derivatives. CHEM LETT 2010. [DOI: 10.1246/cl.2010.726] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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39
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Preus S, Kilså K, Wilhelmsson LM, Albinsson B. Photophysical and structural properties of the fluorescent nucleobase analogues of the tricyclic cytosine (tC) family. Phys Chem Chem Phys 2010; 12:8881-92. [PMID: 20532361 DOI: 10.1039/c000625d] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Fundamental insight into the unique fluorescence and nucleobase-mimicking properties of the fluorescent nucleobase analogues of the tC family is not only vital in explaining the behaviour of these probes in nucleic acid environments, but will also be profitable in the development of new and improved fluorescent base analogues. Here, temperature-dependent fluorescence quantum yield measurements are used to successfully separate and quantify the temperature-dependent and temperature-independent non-radiative excited-state decay processes of the three nucleobase analogues tC, tC(O) and tC(nitro); all of which are derivatives of a phenothiazine or phenoxazine tricyclic framework. These results strongly suggest that the non-radiative decay process dominating the fast deactivation of tC(nitro) is an internal conversion of a different origin than the decay pathways of tC and tC(O). tC(nitro) is reported to be fluorescent only in less dipolar solvents at room temperature, which is explained by an increase in excited-state dipole moment along the main non-radiative decay pathway, a suggestion that applies in the photophysical discussion of large polycyclic nitroaromatics in general. New insight into the ground and excited-state potential energy surfaces of the isolated tC bases is obtained by means of high level DFT and TDDFT calculations. The S(0) potential energy surfaces of tC and tC(nitro) possess two global minima corresponding to geometries folded along the middle sulfur-nitrogen axis separated by an energy barrier of 0.05 eV as calculated at the B3LYP/6-311+G(2d,p) level. The ground-state potential energy surface of tC(O) is also predicted to be shallow along the bending coordinate but with an equilibrium geometry corresponding to the planar conformation of the tricyclic framework, which may explain some of the dissimilar properties of tC and tC(O) in various confined (biological) environments. The S(1) equilibrium geometries of all three base analogues are predicted to be planar. These results are discussed in the context of the tC bases positioned in double-stranded DNA scenarios.
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Affiliation(s)
- Søren Preus
- Department of Chemistry, University of Copenhagen, DK-2100 Copenhagen, Denmark.
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40
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Sinkeldam RW, Greco NJ, Tor Y. Fluorescent analogs of biomolecular building blocks: design, properties, and applications. Chem Rev 2010; 110:2579-619. [PMID: 20205430 PMCID: PMC2868948 DOI: 10.1021/cr900301e] [Citation(s) in RCA: 658] [Impact Index Per Article: 47.0] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Affiliation(s)
- Renatus W. Sinkeldam
- Department of Chemistry and Biochemistry, University of California, San Diego 9500 Gilman Drive, La Jolla, California 92093-0358
| | | | - Yitzhak Tor
- Department of Chemistry and Biochemistry, University of California, San Diego 9500 Gilman Drive, La Jolla, California 92093-0358
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Preus S, Börjesson K, Kilså K, Albinsson B, Wilhelmsson LM. Characterization of nucleobase analogue FRET acceptor tCnitro. J Phys Chem B 2010; 114:1050-6. [PMID: 20039634 DOI: 10.1021/jp909471b] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The fluorescent nucleobase analogues of the tricyclic cytosine (tC) family, tC and tC(O), possess high fluorescence quantum yields and single fluorescence lifetimes, even after incorporation into double-stranded DNA, which make these base analogues particularly useful as fluorescence resonance energy transfer (FRET) probes. Recently, we reported the first all-nucleobase FRET pair consisting of tC(O) as the donor and the novel tC(nitro) as the acceptor. The rigid and well-defined position of this FRET pair inside the DNA double helix, and consequently excellent control of the orientation factor in the FRET efficiency, are very promising features for future studies of nucleic acid structures. Here, we provide the necessary spectroscopic and photophysical characterization of tC(nitro) needed in order to utilize this probe as a FRET acceptor in nucleic acids. The lowest energy absorption band from 375 to 525 nm is shown to be the result of a single in-plane polarized electronic transition oriented approximately 27 degrees from the molecular long axis. This band overlaps the emission bands of both tC and tC(O), and the Forster characteristics of these donor-acceptor pairs are calculated for double-stranded DNA scenarios. In addition, the UV-vis absorption of tC(nitro) is monitored in a broad pH range and the neutral form is found to be totally predominant under physiological conditions with a pK(a) of 11.1. The structure and electronic spectrum of tC(nitro) is further characterized by density functional theory calculations.
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Affiliation(s)
- Søren Preus
- Department of Chemistry, University of Copenhagen, Universitetsparken 5, DK-2100 Copenhagen, Denmark
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42
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Zhang L, Chen X, Liu H, Han L, Cukier RI, Bu Y. Exploration of the Biological Micro-Surrounding Effect on the Excited States of the Size-Expanded Fluorescent Base x-Cytosine in DNA. J Phys Chem B 2010; 114:3726-34. [DOI: 10.1021/jp9117503] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Laibin Zhang
- The Center for Modeling & Simulation Chemistry, Institute of Theoretical Chemistry, Shandong University, Jinan, 250100, P. R. China, and Department of Chemistry, Michigan State University, East Lansing, Michigan 48823
| | - Xiaohua Chen
- The Center for Modeling & Simulation Chemistry, Institute of Theoretical Chemistry, Shandong University, Jinan, 250100, P. R. China, and Department of Chemistry, Michigan State University, East Lansing, Michigan 48823
| | - Haiying Liu
- The Center for Modeling & Simulation Chemistry, Institute of Theoretical Chemistry, Shandong University, Jinan, 250100, P. R. China, and Department of Chemistry, Michigan State University, East Lansing, Michigan 48823
| | - Li Han
- The Center for Modeling & Simulation Chemistry, Institute of Theoretical Chemistry, Shandong University, Jinan, 250100, P. R. China, and Department of Chemistry, Michigan State University, East Lansing, Michigan 48823
| | - Robert I. Cukier
- The Center for Modeling & Simulation Chemistry, Institute of Theoretical Chemistry, Shandong University, Jinan, 250100, P. R. China, and Department of Chemistry, Michigan State University, East Lansing, Michigan 48823
| | - Yuxiang Bu
- The Center for Modeling & Simulation Chemistry, Institute of Theoretical Chemistry, Shandong University, Jinan, 250100, P. R. China, and Department of Chemistry, Michigan State University, East Lansing, Michigan 48823
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43
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Real-time observation of the transition from transcription initiation to elongation of the RNA polymerase. Proc Natl Acad Sci U S A 2009; 106:22175-80. [PMID: 20018723 DOI: 10.1073/pnas.0906979106] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The transition from initiation to elongation of the RNA polymerase (RNAP) is an important stage of transcription that often limits the production of the full-length RNA. Little is known about the RNAP transition kinetics and the steps that dictate the transition rate, because of the challenge in monitoring subpopulations of the transient and heterogeneous transcribing complexes in rapid and real time. Here, we have dissected the complete transcription initiation pathway of T7 RNAP by using kinetic modeling of RNA synthesis and by determining the initiation (IC) to elongation (EC) transition kinetics at each RNA polymerization step using single-molecule and stopped-flow FRET methods. We show that the conversion of IC to EC in T7 RNAP consensus promoter occurs only after 8- to 12-nt synthesis, and the 12-nt synthesis represents a critical juncture in the transcriptional initiation pathway when EC formation is most efficient. We show that the slow steps of transcription initiation, including DNA scrunching/RNAP-promoter rotational changes during 5- to 8-nt synthesis, not the major conformational changes, dictate the overall rate of EC formation in T7 RNAP and represent key steps that regulate the synthesis of full-length RNA.
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44
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Mizuta M, Seio K, Ohkubo A, Sekine M. Fluorescence properties of pyrimidopyrimidoindole nucleoside dC(PPI) incorporated into oligodeoxynucleotides. J Phys Chem B 2009; 113:9562-9. [PMID: 19537698 DOI: 10.1021/jp807562c] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A series of oligodeoxynucleotides labeled by a pyrimidopyrimidoindole deoxynucleoside (1a: dC(PPI)) and its derivatives 2a and 3a substituted with electron-donating and -withdrawing groups, respectively, were synthesized according to the phosphoramidite approach. The photophysical properties and quenching efficiencies of oligonucleotides incorporating dC(PPI) derivatives were studied in detail. The thermal denaturation experiments and molecular dynamics simulation of DNA duplexes incorporating dC(PPI) suggested that a modified base of dC(PPI) could form base pairs with guanine and adenine in canonical Watson-Crick and reverse-wobble geometries, respectively. The fluorescence of oligonucleotides incorporating dC(PPI) derivatives increased upon binding to the counter strands, except when dC(PPI) and guanine formed a base pair. It was revealed that dGMP quenched the fluorescence of the cyano derivative 3a most effectively, whereas it affected that of the methoxy derivative 2a least effectively. The involvement of the electron transfer from guanine to the dC(PPI) derivatives in the fluorescence quenching was supported by energy considerations.
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Affiliation(s)
- Masahiro Mizuta
- Department of Life Science, Tokyo Institute of Technology, Nagatsuta, Midoriku, Yokohama 226-8501, Japan
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45
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Zhang L, Li H, Li J, Chen X, Bu Y. Absorption and fluorescence emission spectroscopic characters of naphtho-homologated yy-DNA bases and effect of methanol solution and base pairing. J Comput Chem 2009; 31:825-36. [PMID: 19598267 DOI: 10.1002/jcc.21376] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
A comprehensive theoretical study of electronic transitions of naphtho-homologated base analogs, namely, yy-T, yy-C, yy-A, and yy-G, was performed. The nature of the low-lying excited states is discussed, and the results are compared with those from experiment and also with those of y-bases. Geometrical characteristics of the lowest excited singlet pipi* and npi* states were explored using the CIS method, and the effects of methanol solution and paring with their complementary natural bases on the relevant absorption and emission spectra of these modified bases were examined. The calculated excitation and emission energies agree well with the measured data, where experimental results are available. In methanol solution, the fluorescence from yy-A and yy-G would be expected to occur around 539 and 562 nm, respectively, suggesting that yy-A is a green-colored fluorophore, whereas yy-G is a yellow-colored fluorophore. The methanol solution was found to red-shift both the absorption and emission maxima of yy-A, yy-T, and yy-C, but blue-shift those for yy-G. Generally, though base pairing has no significant effects on the absorption and fluorescence maxima of yy-A, yy-C, and yy-T, it blue-shifts those for yy-G.
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Affiliation(s)
- Laibin Zhang
- The Center for Modeling and Simulation Chemistry, Institute of Theoretical Chemistry, Shandong University, Jinan 250100, People's Republic of China
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Zhang X, Wadkins RM. DNA hairpins containing the cytidine analog pyrrolo-dC: structural, thermodynamic, and spectroscopic studies. Biophys J 2009; 96:1884-91. [PMID: 19254547 DOI: 10.1016/j.bpj.2008.12.3890] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2008] [Accepted: 12/01/2008] [Indexed: 11/16/2022] Open
Abstract
Structures formed by single-strand DNA have become increasingly interesting because of their roles in a number of biological processes, particularly transcription and its regulation. Of particular importance is the fact that antitumor drugs such as Actinomycin D can selectively bind DNA hairpins over fully paired, double-strand DNA. A new fluorescent base analog, pyrrolo-deoxycytidine (PdC), can now be routinely incorporated into single-strand DNA. The fluorescence of PdC is particularly useful for studying the formation of single-strand DNA in regions of double-strand DNA. The fluorescence is quenched when PdC is paired with a complementary guanine residue, and thus is greatly enhanced upon formation of single-strand DNA. Hence, any process that results in melting or opening of DNA strands produces an increase in the fluorescence intensity of this base analog. In this study we measured the structural effects of incorporating PdC into DNA hairpins, and the effect of this incorporation on the binding of the hairpins by a fluorescent analog of the drug Actinomycin D. Two hairpin DNAs were used: one with PdC in the stem (basepaired) and one with PdC in the loop (unpaired). The thermal stability, 7-aminoactinomycin D binding, and three-dimensional structures of PdC incorporated into these DNA hairpins were all quite similar as compared to the hairpins containing an unmodified dC residue. Fluorescence lifetime measurements indicate that two lifetimes are present in PdC, and that the increase in fluorescence of the unpaired PdC residue compared to the basepaired PdC is due to an increase in the contribution of the longer lifetime to the average fluorescence lifetime. Our data indicate that PdC can be used effectively to differentiate paired and unpaired bases in DNA hairpin secondary structures, and should be similarly applicable for related structures such as cruciforms and quadruplexes. Further, our data indicate that PdC can act as a fluorescence resonance energy transfer donor for the fluorescent drug 7-aminoactinomycin D.
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Affiliation(s)
- Xu Zhang
- Department of Chemistry and Biochemistry, University of Mississippi, University, Mississippi, USA
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Zhang L, Li H, Chen X, Cukier RI, Bu Y. Absorption and fluorescence emission spectroscopic characters of size-expanded yDNA bases and effect of deoxyribose and base pairing. J Phys Chem B 2009; 113:1173-81. [PMID: 19159339 DOI: 10.1021/jp8094648] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
We present an ab initio study of the optical absorption and emission spectra of size-expanded nucleic acid base analogues (yA, yT, yT-m, yG, yG-t2, and yC) obtained by benzo homologation (see Krueger, A. T.; Lu, H.; Lee, A. H. F.; Kool, E. T. Acc. Chem. Res. 2007, 40, 141 and references therein). Also examined were the effects of linking to deoxyribose and hydrogen bonding to their natural complementary bases (T, A, C, and G, respectively). The calculated excitation and emission energies are in good agreement with the measured data where experimental results are available. The geometries corresponding to the first excited singlet state of yA and yT are found to be quasi-planar, while those for yG and yC are nonplanar. In general, binding to deoxyribose will red shift the absorbance and fluorescence emission maxima of the y-bases. The ground-state geometries of the Watson-Crick analog base pairs (yAT, yTA, yGC, and yCG) are found to be planar, and the calculated interaction energies are very close to those of natural base pairs, indicating that the y-bases can pair with their natural complementary partners to generate stable base pairs. The base pairing has no significant effects on the fluorescence emission of yA, yC, and yT, but blue shifts the fluorescence emission of yG by 22 nm.
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Affiliation(s)
- Laibin Zhang
- The Center for Modeling and Simulation Chemistry, Institute of Theoretical Chemistry, Shandong University, Jinan, 250100, People's Republic of China
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Spectroscopic studies of position-specific DNA "breathing" fluctuations at replication forks and primer-template junctions. Proc Natl Acad Sci U S A 2009; 106:4231-6. [PMID: 19246398 DOI: 10.1073/pnas.0900803106] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Junctions between ssDNA and dsDNA sequences are important in many cellular processes, including DNA replication, transcription, recombination, and repair. Significant transient conformational fluctuations ("DNA breathing") can occur at these ssDNA-dsDNA junctions. The involvement of such breathing in the mechanisms of macromolecular complexes that operate at these loci is not well understood, in part because these fluctuations have been difficult to measure in a position-specific manner. To address this issue we constructed forked or primer-template DNA constructs with 1 or 2 adjacent 2-aminopurine (2-AP) nucleotide residues (adenine analogues) placed at specific positions on both sides of the ssDNA-dsDNA junction. Unlike canonical DNA bases, 2-AP absorbs, fluoresces, and displays CD spectra at wavelengths >300 nm, where other nucleic acid and protein components are transparent. We used CD and fluorescence spectra and acrylamide quenching of these probes to monitor the extent and nature of DNA breathing of A-T base pairs at specific positions around the ssDNA-dsDNA junction. As expected, spectroscopically measurable unwinding penetrates approximately 2 bp into the duplex region of these junctions under physiological conditions for the constructs examined. Surprisingly, we found that 2-AP bases at ssDNA sites directly adjacent to ssDNA-dsDNA junctions are significantly more unstacked than those at more distant ssDNA positions. These local and transient DNA conformations on both sides of ssDNA-dsDNA junctions may serve as specific interaction targets for enzymes that manipulate DNA in the processes of gene expression.
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49
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Ends free and self-quenched molecular beacon with pyrene labeled pyrrolocytidine in the middle of the stem. Tetrahedron 2009. [DOI: 10.1016/j.tet.2008.10.093] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
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50
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Abstract
Transfer RNA (tRNA) molecules mediate translation of the nucleic acid genetic code into the amino acid building blocks of proteins, thus ensuring the survivability of cells. The dynamic properties of tRNA molecules are crucial to their functions in both activity and specificity. This chapter summarizes two methods that have been recently developed or improved upon previous protocols to introduce fluorophores to site-specific positions in tRNA. One method enables incorporation of fluorophores carrying a primary amine (such as proflavin or rhodamine) to dihydrouridine (D) residues in the tRNA tertiary core, and a second method enables incorporation of pyrroloC and 2-aminopurine to positions 75 and 76, respectively, of the CCA sequence at the 3' end. These site-specific fluorophore labeling methods utilize tRNA transcripts as the substrates to provide the versatility with both wild-type and mutant sequences for examining their motions in space and time during the process of decoding genetic information.
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Affiliation(s)
- Cuiping Liu
- Department of Biochemistry and Molecular Biology, Thomas Jefferson University, Philadelphia, Pennsylvania, USA
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