1
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Riback JA, Eeftens JM, Lee DSW, Quinodoz SA, Donlic A, Orlovsky N, Wiesner L, Beckers L, Becker LA, Strom AR, Rana U, Tolbert M, Purse BW, Kleiner R, Kriwacki R, Brangwynne CP. Viscoelasticity and advective flow of RNA underlies nucleolar form and function. Mol Cell 2023; 83:3095-3107.e9. [PMID: 37683610 PMCID: PMC11089468 DOI: 10.1016/j.molcel.2023.08.006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2022] [Revised: 04/20/2023] [Accepted: 08/08/2023] [Indexed: 09/10/2023]
Abstract
The nucleolus is the largest biomolecular condensate and facilitates transcription, processing, and assembly of ribosomal RNA (rRNA). Although nucleolar function is thought to require multiphase liquid-like properties, nucleolar fluidity and its connection to the highly coordinated transport and biogenesis of ribosomal subunits are poorly understood. Here, we use quantitative imaging, mathematical modeling, and pulse-chase nucleotide labeling to examine nucleolar material properties and rRNA dynamics. The mobility of rRNA is several orders of magnitude slower than that of nucleolar proteins, with rRNA steadily moving away from the transcriptional sites in a slow (∼1 Å/s), radially directed fashion. This constrained but directional mobility, together with polymer physics-based calculations, suggests that nascent rRNA forms an entangled gel, whose constant production drives outward flow. We propose a model in which progressive maturation of nascent rRNA reduces its initial entanglement, fluidizing the nucleolar periphery to facilitate the release of assembled pre-ribosomal particles.
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Affiliation(s)
- Joshua A Riback
- Department of Chemical and Biological Engineering, Princeton University, Princeton, NJ 08544, USA
| | - Jorine M Eeftens
- Department of Chemical and Biological Engineering, Princeton University, Princeton, NJ 08544, USA
| | - Daniel S W Lee
- Department of Chemical and Biological Engineering, Princeton University, Princeton, NJ 08544, USA; Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, Princeton, NJ 08544, USA
| | - Sofia A Quinodoz
- Department of Chemical and Biological Engineering, Princeton University, Princeton, NJ 08544, USA
| | - Anita Donlic
- Department of Chemical and Biological Engineering, Princeton University, Princeton, NJ 08544, USA
| | - Natalia Orlovsky
- Department of Molecular Biology, Princeton University, Princeton, Princeton, NJ 08544, USA
| | - Lennard Wiesner
- Department of Chemical and Biological Engineering, Princeton University, Princeton, NJ 08544, USA
| | - Lien Beckers
- Department of Chemical and Biological Engineering, Princeton University, Princeton, NJ 08544, USA; Howard Hughes Medical Institute, Princeton University, Princeton, Princeton, NJ 08544, USA
| | - Lindsay A Becker
- Department of Chemical and Biological Engineering, Princeton University, Princeton, NJ 08544, USA; Howard Hughes Medical Institute, Princeton University, Princeton, Princeton, NJ 08544, USA
| | - Amy R Strom
- Department of Chemical and Biological Engineering, Princeton University, Princeton, NJ 08544, USA
| | - Ushnish Rana
- Department of Chemical and Biological Engineering, Princeton University, Princeton, NJ 08544, USA
| | - Michele Tolbert
- Department of Structural Biology, St. Jude Children's Research Hospital, Memphis, TN 38103, USA
| | - Byron W Purse
- Department of Chemistry and Biochemistry and the Viral Information Institute, San Diego State University, San Diego, CA 92182, USA
| | - Ralph Kleiner
- Department of Chemistry, Princeton University, Princeton, Princeton, NJ 08544, USA
| | - Richard Kriwacki
- Department of Structural Biology, St. Jude Children's Research Hospital, Memphis, TN 38103, USA
| | - Clifford P Brangwynne
- Department of Chemical and Biological Engineering, Princeton University, Princeton, NJ 08544, USA; Princeton Institute for the Science and Technology of Materials, Princeton University, Princeton, Princeton, NJ 08544, USA; Howard Hughes Medical Institute, Princeton University, Princeton, Princeton, NJ 08544, USA; Omenn-Darling Bioengineering Institute, Princeton University, Princeton, NJ 08544, USA.
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2
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Yewdall NA, André AAM, van Haren MHI, Nelissen FHT, Jonker A, Spruijt E. ATP:Mg 2+ shapes material properties of protein-RNA condensates and their partitioning of clients. Biophys J 2022; 121:3962-3974. [PMID: 36004782 PMCID: PMC9674983 DOI: 10.1016/j.bpj.2022.08.025] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2022] [Revised: 07/29/2022] [Accepted: 08/19/2022] [Indexed: 11/26/2022] Open
Abstract
Many cellular condensates are heterotypic mixtures of proteins and RNA formed in complex environments. Magnesium ions (Mg2+) and ATP can impact RNA folding, and local intracellular levels of these factors can vary significantly. However, the effect of ATP:Mg2+ on the material properties of protein-RNA condensates is largely unknown. Here, we use an in vitro condensate model of nucleoli, made from nucleophosmin 1 (NPM1) proteins and ribosomal RNA (rRNA), to study the effect of ATP:Mg2+. While NPM1 dynamics remain unchanged at increasing Mg2+ concentrations, the internal RNA dynamics dramatically slowed until a critical point, where gel-like states appeared, suggesting the RNA component alone forms a viscoelastic network that undergoes maturation driven by weak multivalent interactions. ATP reverses this arrest and liquefies the gel-like structures. ATP:Mg2+ also influenced the NPM1-rRNA composition of condensates and enhanced the partitioning of two clients: an arginine-rich peptide and a small nuclear RNA. By contrast, larger ribosome partitioning shows dependence on ATP:Mg2+ and can become reversibly trapped around NPM1-rRNA condensates. Lastly, we show that dissipative enzymatic reactions that deplete ATP can be used to control the shape, composition, and function of condensates. Our results illustrate how intracellular environments may regulate the state and client partitioning of RNA-containing condensates.
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Affiliation(s)
- N Amy Yewdall
- Institute for Molecules and Materials, Radboud University, Nijmegen, the Netherlands.
| | - Alain A M André
- Institute for Molecules and Materials, Radboud University, Nijmegen, the Netherlands
| | - Merlijn H I van Haren
- Institute for Molecules and Materials, Radboud University, Nijmegen, the Netherlands
| | - Frank H T Nelissen
- Institute for Molecules and Materials, Radboud University, Nijmegen, the Netherlands
| | - Aafke Jonker
- Institute for Molecules and Materials, Radboud University, Nijmegen, the Netherlands
| | - Evan Spruijt
- Institute for Molecules and Materials, Radboud University, Nijmegen, the Netherlands.
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3
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Translation initiation site of mRNA is selected through dynamic interaction with the ribosome. Proc Natl Acad Sci U S A 2022; 119:e2118099119. [PMID: 35605125 DOI: 10.1073/pnas.2118099119] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
SignificanceRibosomes translate the genetic codes of messenger RNA (mRNA) to make proteins. Translation must begin at the correct initiation site; otherwise, abnormal proteins will be produced. Here, we show that a short ribosome-specific sequence in the upstream followed by an unstructured downstream sequence is a favorable initiation site. Those mRNAs lacking either of these two characteristics do not associate tightly with the ribosome. Initiator transfer RNA (tRNA) and initiation factors facilitate the binding. However, when the downstream site forms structures, initiation factor 3 triggers the dissociation of the accommodated initiator tRNA and the subsequent disassembly of the ribosome-mRNA complex. Thus, initiation factors help the ribosome distinguish unfavorable structured sequences that may not act as the mRNA translation initiation site.
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4
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Kumar S, Reddy G. TPP Riboswitch Populates Holo-Form-like Structure Even in the Absence of Cognate Ligand at High Mg 2+ Concentration. J Phys Chem B 2022; 126:2369-2381. [PMID: 35298161 DOI: 10.1021/acs.jpcb.1c10794] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Riboswitches are noncoding RNA that regulate gene expression by folding into specific three-dimensional structures (holo-form) upon binding by their cognate ligand in the presence of Mg2+. Riboswitch functioning is also hypothesized to be under kinetic control requiring large cognate ligand concentrations. We ask the question under thermodynamic conditions, can the riboswitches populate structures similar to the holo-form only in the presence of Mg2+ and absence of cognate ligand binding. We addressed this question using thiamine pyrophosphate (TPP) riboswitch as a model system and computer simulations using a coarse-grained model for RNA. The folding free energy surface (FES) shows that with the initial increase in Mg2+ concentration ([Mg2+]), the aptamer domain (AD) of TPP riboswitch undergoes a barrierless collapse in its dimensions. On further increase in [Mg2+], intermediates separated by barriers appear on the FES, and one of the intermediates has a TPP ligand-binding competent structure. We show that site-specific binding of the Mg2+ aids in the formation of tertiary contacts. For [Mg2+] greater than physiological concentration, AD folds into a structure similar to the crystal structure of the TPP holo-form even in the absence of the TPP ligand. The folding kinetics shows that TPP AD populates an intermediate due to the misalignment of two arms present in the structure, which acts as a kinetic trap, leading to larger folding timescales. The predictions of the intermediate structures from the simulations are amenable for experimental verification.
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Affiliation(s)
- Sunil Kumar
- Solid State and Structural Chemistry Unit, Indian Institute of Science, Bengaluru, Karnataka 560012, India
| | - Govardhan Reddy
- Solid State and Structural Chemistry Unit, Indian Institute of Science, Bengaluru, Karnataka 560012, India
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5
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Armstrong RE, Horáček M, Zijlstra P. Plasmonic Assemblies for Real-Time Single-Molecule Biosensing. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2020; 16:e2003934. [PMID: 33258287 DOI: 10.1002/smll.202003934] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/29/2020] [Revised: 10/09/2020] [Indexed: 05/11/2023]
Abstract
Their tunable optical properties and versatile surface functionalization have sparked applications of plasmonic assemblies in the fields of biosensing, nonlinear optics, and photonics. Particularly, in the field of biosensing, rapid advances have occurred in the use of plasmonic assemblies for real-time single-molecule sensing. Compared to individual particles, the use of assemblies as sensors provides stronger signals, more control over the optical properties, and access to a broader range of timescales. In the past years, they have been used to directly reveal single-molecule interactions, mechanical properties, and conformational dynamics. This review summarizes the development of real-time single-molecule sensors built around plasmonic assemblies. First, a brief overview of their optical properties is given, and then recent applications are described. The current challenges in the field and suggestions to overcome those challenges are discussed in detail. Their stability, specificity, and sensitivity as sensors provide a complementary approach to other single-molecule techniques like force spectroscopy and single-molecule fluorescence. In future applications, the impact in real-time sensing on ultralong timescales (hours) and ultrashort timescales (sub-millisecond), time windows that are difficult to access using other techniques, is particularly foreseen.
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Affiliation(s)
- Rachel E Armstrong
- Department of Applied Physics & Institute for Complex Molecular Systems, Eindhoven University of Technology, Postbus 513, Eindhoven, MB, 5600, the Netherlands
| | - Matěj Horáček
- Department of Applied Physics & Institute for Complex Molecular Systems, Eindhoven University of Technology, Postbus 513, Eindhoven, MB, 5600, the Netherlands
| | - Peter Zijlstra
- Department of Applied Physics & Institute for Complex Molecular Systems, Eindhoven University of Technology, Postbus 513, Eindhoven, MB, 5600, the Netherlands
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6
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Statistical physics and mesoscopic modeling to interpret tethered particle motion experiments. Methods 2019; 169:57-68. [PMID: 31302177 DOI: 10.1016/j.ymeth.2019.07.006] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2019] [Revised: 06/11/2019] [Accepted: 07/07/2019] [Indexed: 11/22/2022] Open
Abstract
Tethered particle motion experiments are versatile single-molecule techniques enabling one to address in vitro the molecular properties of DNA and its interactions with various partners involved in genetic regulations. These techniques provide raw data such as the tracked particle amplitude of movement, from which relevant information about DNA conformations or states must be recovered. Solving this inverse problem appeals to specific theoretical tools that have been designed in the two last decades, together with the data pre-processing procedures that ought to be implemented to avoid biases inherent to these experimental techniques. These statistical tools and models are reviewed in this paper.
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7
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Ganguly A, Das S. Compaction-induced strengthening of intercalation within RNA double helices at high ionic strength of the medium: Spectral elucidation and anomalous thermodynamics. J Mol Liq 2019. [DOI: 10.1016/j.molliq.2019.04.004] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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8
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Abstract
Multiplex detection of biomolecules is important in bionanotechnology and clinical diagnostics. Multiplexing using engineered solutions such as microarrays, synthetic nanopores, and DNA barcodes is promising, but they require sophisticated design/engineering and typically yield semiquantitative information. Single-molecule fluorescence resonance energy transfer (smFRET) is an attractive tool in this regard as it enables both sensitive and quantitative detection. However, multiplexing with smFRET remains a great challenge as it requires either multiple excitation sources, an antenna system created by multiple FRET pairs, or multiple acceptors of the donor fluorophore, which complicates not only the labeling schemes but also data analysis, due to overlapping of FRET efficiencies ( EFRET). Here, we address these currently outstanding issues by designing interconvertible hairpin-based sensors (iHabSs) with nonoverlapping EFRET utilizing a single donor/acceptor pair and demonstrate a high-confidence multiplex detection of unlabeled nucleic acid sequences. We validated the reliability of our approach by systematically omitting one target at a time. Further, we demonstrate that these iHabSs are fully recyclable, sensitive with a limit of detection of ∼200 pM, and able to discriminate against single base mismatches. The multiplexed approach developed here has the potential to benefit the fields of biosensing and diagnostics by allowing simultaneous and quantitative detection of unlabeled nucleic acid biomarkers.
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Affiliation(s)
- Anisa Kaur
- Department of Chemistry, Virginia Commonwealth University, 1001 West Main Street, Richmond, Virginia 23284, United States
| | - Kumar Sapkota
- Department of Chemistry, Virginia Commonwealth University, 1001 West Main Street, Richmond, Virginia 23284, United States
| | - Soma Dhakal
- Department of Chemistry, Virginia Commonwealth University, 1001 West Main Street, Richmond, Virginia 23284, United States
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9
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Fan HF, Ma CH, Jayaram M. Single-Molecule Tethered Particle Motion: Stepwise Analyses of Site-Specific DNA Recombination. MICROMACHINES 2018; 9:E216. [PMID: 30424148 PMCID: PMC6187709 DOI: 10.3390/mi9050216] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/15/2018] [Revised: 04/25/2018] [Accepted: 04/28/2018] [Indexed: 12/17/2022]
Abstract
Tethered particle motion/microscopy (TPM) is a biophysical tool used to analyze changes in the effective length of a polymer, tethered at one end, under changing conditions. The tether length is measured indirectly by recording the Brownian motion amplitude of a bead attached to the other end. In the biological realm, DNA, whose interactions with proteins are often accompanied by apparent or real changes in length, has almost exclusively been the subject of TPM studies. TPM has been employed to study DNA bending, looping and wrapping, DNA compaction, high-order DNA⁻protein assembly, and protein translocation along DNA. Our TPM analyses have focused on tyrosine and serine site-specific recombinases. Their pre-chemical interactions with DNA cause reversible changes in DNA length, detectable by TPM. The chemical steps of recombination, depending on the substrate and the type of recombinase, may result in a permanent length change. Single molecule TPM time traces provide thermodynamic and kinetic information on each step of the recombination pathway. They reveal how mechanistically related recombinases may differ in their early commitment to recombination, reversibility of individual steps, and in the rate-limiting step of the reaction. They shed light on the pre-chemical roles of catalytic residues, and on the mechanisms by which accessory proteins regulate recombination directionality.
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Affiliation(s)
- Hsiu-Fang Fan
- Biophotonics and Molecular Imaging Center, Department of Life Sciences and Institute of Genome Sciences, National Yang-Ming University, Taipei 112, Taiwan.
- Institute of Cellular and Organismic Biology, Academia Sinica, Taipei 115, Taiwan.
| | - Chien-Hui Ma
- Department of Molecular Biosciences, University of Texas at Austin, Austin, TX 78712, USA.
| | - Makkuni Jayaram
- Department of Molecular Biosciences, University of Texas at Austin, Austin, TX 78712, USA.
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10
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Wang FH, Wu YY, Tan ZJ. Salt contribution to the flexibility of single-stranded nucleic acid offinite length. Biopolymers 2016; 99:370-81. [PMID: 23529689 DOI: 10.1002/bip.22189] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2012] [Accepted: 11/18/2012] [Indexed: 12/15/2022]
Abstract
Nucleic acids are negatively charged macromolecules and their structure properties are strongly coupled to metal ions in solutions. In this article, the salt effects on the flexibility of single-stranded (ss) nucleic acid chain ranging from 12 to 120 nucleotides are investigated systematically by the coarse-grained Monte Carlo simulations where the salt ions are considered explicitly and the ss chain is modeled with the virtual-bond structural model. Our calculations show that, the increase of ion concentration causes the structural collapse of ss chain and multivalent ions are much more efficient in causing such collapse, and both trivalent/small divalent ions can induce more compact state than a random relaxation state. We found that monovalent, divalent, and trivalent ions can all overcharge ss chain, and the dominating source for such overcharging changes from ion-exclusion-volume effect to ion Coulomb correlations. In addition, the predicted Na(+) and Mg(2+)-dependent persistence length l(p)'s of ss nucleic acid are in accordance with the available experimental data, and through systematic calculations, we obtained the empirical formulas for l(p) as a function of [Na(+)], [Mg(2+)] and chain length.
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Affiliation(s)
- Feng-Hua Wang
- Department of Physics and Key Laboratory of Artificial Micro- and Nano-structures of Ministry of Education, School of Physics and Technology, Wuhan University, Wuhan, 430072, China
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11
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Hidalgo-Soria M, Pérez-Madrid A, Santamaría-Holek I. Effect of elastic colored noise in the hopping dynamics of single molecules in stretching experiments. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2015; 92:062708. [PMID: 26764728 DOI: 10.1103/physreve.92.062708] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/16/2015] [Indexed: 06/05/2023]
Abstract
The influence of colored noise induced by elastic fluctuations in single-molecule stretching experiments is theoretically and numerically studied. Unlike in the thermal white noise case currently considered in the literature, elastically induced hopping dynamics between folded and unfolded states is manifested through critical oscillations showing smaller end-to-end distance fluctuations (δx∼1.25nm) within the free energy wells corresponding to both states. Our results are derived by analyzing the elastic coupling between the Handle-Molecule-Handle system and the laser optical tweezers (LOT) array. It is shown that an Ornstein-Uhlenbeck process related to this elastic coupling may trigger the hopping transitions via a colored noise with an intensity proportional to the elastic constant of the LOT array. Evolution equations of the variables of the system were derived by using the irreversible thermodynamics of small systems recently proposed. Theoretical expressions for the corresponding stationary probability densities are provided and the viability of inferring the shape of the free energy from direct measurements is discussed.
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Affiliation(s)
- M Hidalgo-Soria
- UMDI, Facultad de Ciencias, Universidad Nacional Autónoma de México, Campus Juriquilla, Querétaro 76230, México
| | - A Pérez-Madrid
- Departament de Física Fonamental, Facultat de Física, Universitat de Barcelona, Marti i Franques, E-08028 Barcelona, Spain
| | - I Santamaría-Holek
- UMDI, Facultad de Ciencias, Universidad Nacional Autónoma de México, Campus Juriquilla, Querétaro 76230, México
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12
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Kahlscheuer ML, Widom J, Walter NG. Single-Molecule Pull-Down FRET to Dissect the Mechanisms of Biomolecular Machines. Methods Enzymol 2015; 558:539-570. [PMID: 26068753 PMCID: PMC4886477 DOI: 10.1016/bs.mie.2015.01.009] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Spliceosomes are multimegadalton RNA-protein complexes responsible for the faithful removal of noncoding segments (introns) from pre-messenger RNAs (pre-mRNAs), a process critical for the maturation of eukaryotic mRNAs for subsequent translation by the ribosome. Both the spliceosome and ribosome, as well as many other RNA and DNA processing machineries, contain central RNA components that endow biomolecular complexes with precise, sequence-specific nucleic acid recognition, and versatile structural dynamics. Single-molecule fluorescence (or Förster) resonance energy transfer (smFRET) microscopy is a powerful tool for the study of local and global conformational changes of both simple and complex biomolecular systems involving RNA. The integration of biochemical tools such as immunoprecipitation with advanced methods in smFRET microscopy and data analysis has opened up entirely new avenues toward studying the mechanisms of biomolecular machines isolated directly from complex biological specimens, such as cell extracts. Here, we detail the general steps for using prism-based total internal reflection fluorescence microscopy in exemplary single-molecule pull-down FRET studies of the yeast spliceosome and discuss the broad application potential of this technique.
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Affiliation(s)
- Matthew L Kahlscheuer
- Single Molecule Analysis Group, Department of Chemistry, University of Michigan, Ann Arbor, Michigan, USA
| | - Julia Widom
- Single Molecule Analysis Group, Department of Chemistry, University of Michigan, Ann Arbor, Michigan, USA
| | - Nils G Walter
- Single Molecule Analysis Group, Department of Chemistry, University of Michigan, Ann Arbor, Michigan, USA.
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13
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Revalee JD, Blab GA, Wilson HD, Kahn JD, Meiners JC. Tethered particle motion reveals that LacI·DNA loops coexist with a competitor-resistant but apparently unlooped conformation. Biophys J 2014; 106:705-15. [PMID: 24507611 DOI: 10.1016/j.bpj.2013.12.024] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2013] [Revised: 11/26/2013] [Accepted: 12/12/2013] [Indexed: 10/25/2022] Open
Abstract
The lac repressor protein (LacI) efficiently represses transcription of the lac operon in Escherichia coli by binding to two distant operator sites on the bacterial DNA and causing the intervening DNA to form a loop. We employed single-molecule tethered particle motion to observe LacI-mediated loop formation and breakdown in DNA constructs that incorporate optimized operator binding sites and intrinsic curvature favorable to loop formation. Previous bulk competition assays indirectly measured the loop lifetimes in these optimized DNA constructs as being on the order of days; however, we measured these same lifetimes to be on the order of minutes for both looped and unlooped states. In a range of single-molecule DNA competition experiments, we found that the resistance of the LacI-DNA complex to competitive binding is a function of both the operator strength and the interoperator sequence. To explain these findings, we present what we believe to be a new kinetic model of loop formation and DNA competition. In this proposed new model, we hypothesize a new unlooped state in which the unbound DNA-binding domain of the LacI protein interacts nonspecifically with nonoperator DNA adjacent to the operator site at which the second LacI DNA-binding domain is bound.
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Affiliation(s)
- Joel D Revalee
- Department of Physics, University of Michigan, Ann Arbor, Michigan
| | - Gerhard A Blab
- Debye Institute, Molecular Biophysics, Utrecht University, Utrecht, The Netherlands
| | - Henry D Wilson
- LSA Biophysics, University of Michigan, Ann Arbor, Michigan
| | - Jason D Kahn
- Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland
| | - Jens-Christian Meiners
- Department of Physics, University of Michigan, Ann Arbor, Michigan; LSA Biophysics, University of Michigan, Ann Arbor, Michigan.
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14
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Gebhard LG, Incicco JJ, Smal C, Gallo M, Gamarnik AV, Kaufman SB. Monomeric nature of dengue virus NS3 helicase and thermodynamic analysis of the interaction with single-stranded RNA. Nucleic Acids Res 2014; 42:11668-86. [PMID: 25223789 PMCID: PMC4191397 DOI: 10.1093/nar/gku812] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Dengue virus nonstructural protein 3 (NS3) is a multifunctional protein formed by a superfamily-2 RNA helicase linked to a protease domain. In this work, we report results from in vitro experiments designed to determine the oligomeric state of dengue virus NS3 helicase (NS3h) and to characterize fundamental properties of the interaction with single-stranded (ss)RNA. Pulsed field gradient-NMR spectroscopy was used to determine the effective hydrodynamic radius of NS3h, which was constant over a wide range of protein concentrations in the absence and presence of ssRNA. Size exclusion chromatography-static light scattering experiments showed that NS3h eluted as a monomeric molecule even in the presence of ssRNA. Binding of NS3h to ssRNA was studied by quantitative fluorescence titrations using fluorescein-labeled and unlabeled ssRNA oligonucleotides of different lengths, and the effect of the fluorescein label on the interaction parameters was also analyzed. Experimental results were well described by a statistical thermodynamic model based on the theory of non-specific interactions of large ligands to a one-dimensional lattice. We found that binding of NS3h to ssRNA oligonucleotides and to poly(A) is characterized by minimum and occluded binding site sizes both of 10 nucleotides and by a weak positive cooperativity between adjacent proteins.
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Affiliation(s)
- Leopoldo G Gebhard
- Fundación Instituto Leloir-Consejo Nacional de Investigaciones Científicas y Técnicas, Ciudad Autónoma de Buenos Aires, C1405BWE, Argentina
| | - J Jeremías Incicco
- Instituto de Química y Fisicoquímica Biológicas and Departamento de Química Biológica, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, Ciudad Autónoma de Buenos Aires, C1113AAD, Argentina
| | - Clara Smal
- Fundación Instituto Leloir-Consejo Nacional de Investigaciones Científicas y Técnicas, Ciudad Autónoma de Buenos Aires, C1405BWE, Argentina
| | - Mariana Gallo
- Fundación Instituto Leloir-Consejo Nacional de Investigaciones Científicas y Técnicas, Ciudad Autónoma de Buenos Aires, C1405BWE, Argentina
| | - Andrea V Gamarnik
- Fundación Instituto Leloir-Consejo Nacional de Investigaciones Científicas y Técnicas, Ciudad Autónoma de Buenos Aires, C1405BWE, Argentina
| | - Sergio B Kaufman
- Instituto de Química y Fisicoquímica Biológicas and Departamento de Química Biológica, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, Ciudad Autónoma de Buenos Aires, C1113AAD, Argentina
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15
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Pitchiaya S, Heinicke LA, Custer TC, Walter NG. Single molecule fluorescence approaches shed light on intracellular RNAs. Chem Rev 2014; 114:3224-65. [PMID: 24417544 PMCID: PMC3968247 DOI: 10.1021/cr400496q] [Citation(s) in RCA: 64] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Affiliation(s)
- Sethuramasundaram Pitchiaya
- Single Molecule Analysis in Real-Time (SMART)
Center, University of Michigan, Ann Arbor, MI 48109-1055, USA
- Single Molecule Analysis Group, Department of
Chemistry, University of Michigan, Ann Arbor, MI 48109-1055, USA
| | - Laurie A. Heinicke
- Single Molecule Analysis Group, Department of
Chemistry, University of Michigan, Ann Arbor, MI 48109-1055, USA
| | - Thomas C. Custer
- Program in Chemical Biology, University of Michigan,
Ann Arbor, MI 48109-1055, USA
| | - Nils G. Walter
- Single Molecule Analysis in Real-Time (SMART)
Center, University of Michigan, Ann Arbor, MI 48109-1055, USA
- Single Molecule Analysis Group, Department of
Chemistry, University of Michigan, Ann Arbor, MI 48109-1055, USA
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Todd GC, Walter NG. Secondary structure of bacteriophage T4 gene 60 mRNA: implications for translational bypassing. RNA (NEW YORK, N.Y.) 2013; 19:685-700. [PMID: 23492219 PMCID: PMC3677283 DOI: 10.1261/rna.037291.112] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
Translational bypassing is a unique phenomenon of bacteriophage T4 gene 60 mRNA wherein the bacterial ribosome produces a single polypeptide chain from a discontinuous open reading frame (ORF). Upon reaching the 50-nucleotide untranslated region, or coding gap, the ribosome either dissociates or bypasses the interruption to continue translating the remainder of the ORF, generating a subunit of a type II DNA topoisomerase. Mutational and computational analyses have suggested that a compact structure, including a stable hairpin, forms in the coding gap to induce bypassing, yet direct evidence is lacking. Here we have probed the secondary structure of gene 60 mRNA with both Tb³⁺ ions and the selective 2'-hydroxyl acylation analyzed by primer extension (SHAPE) reagent 1M7 under conditions where bypassing is observed. The resulting experimentally informed secondary structure models strongly support the presence of the predicted coding gap hairpin and highlight the benefits of using Tb³⁺ as a second, complementary probing reagent. Contrary to several previously proposed models, however, the rest of the coding gap is highly reactive with both probing reagents, suggesting that it forms only a short stem-loop. Mutational analyses coupled with functional assays reveal that two possible base-pairings of the coding gap with other regions of the mRNA are not required for bypassing. Such structural autonomy of the coding gap is consistent with its recently discovered role as a mobile genetic element inserted into gene 60 mRNA to inhibit cleavage by homing endonuclease MobA.
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Affiliation(s)
- Gabrielle C. Todd
- Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109-1055, USA
- Program in Chemical Biology, University of Michigan, Ann Arbor, Michigan 48109-1055, USA
| | - Nils G. Walter
- Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109-1055, USA
- Corresponding authorE-mail
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17
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Jung YJ, Albrecht JA, Kwak JW, Park JW. Direct quantitative analysis of HCV RNA by atomic force microscopy without labeling or amplification. Nucleic Acids Res 2012; 40:11728-36. [PMID: 23074195 PMCID: PMC3526272 DOI: 10.1093/nar/gks953] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Force-based atomic force microscopy (AFM) was used to detect HCV (hepatitis C virus) RNA directly and to quantitatively analyse it without the need for reverse transcription or amplification. Capture and detection DNA probes were designed. The former was spotted onto a substrate with a conventional microarrayer, and the latter was immobilized on an AFM probe. To control the spacing between the immobilized DNAs on the surface, dendron self-assembly was employed. Force-distance curves showed that the mean force of the specific unbinding events was 32 ± 5 pN, and the hydrodynamic distance of the captured RNA was 30-60 nm. Adhesion force maps were generated with criteria including the mean force value, probability of obtaining the specific curves and hydrodynamic distance. The maps for the samples whose concentrations ranged from 0.76 fM to 6.0 fM showed that cluster number has a linear relationship with RNA concentration, while the difference between the observed number and the calculated one increased at low concentrations. Because the detection limit is expected to be enhanced by a factor of 10 000 when a spot of 1 micron diameter is employed, it is believed that HCV RNA of a few copy numbers can be detected by the use of AFM.
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Affiliation(s)
- Yu Jin Jung
- Nanogea Corporation, 6162 Bristol Parkway, Culver City, CA 90230, USA.
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18
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Lamichhane R, Solem A, Black W, Rueda D. Single-molecule FRET of protein-nucleic acid and protein-protein complexes: surface passivation and immobilization. Methods 2010; 52:192-200. [PMID: 20554047 PMCID: PMC3321382 DOI: 10.1016/j.ymeth.2010.06.010] [Citation(s) in RCA: 87] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2010] [Indexed: 11/23/2022] Open
Abstract
Single-molecule fluorescence spectroscopy reveals the real time dynamics that occur during biomolecular interactions that would otherwise be hidden by the ensemble average. It also removes the requirement to synchronize reactions, thus providing a very intuitive approach to study kinetics of biological systems. Surface immobilization is commonly used to increase observation times to the minute time scale, but it can be detrimental if the sample interacts non-specifically with the surface. Here, we review detailed protocols to prevent such interactions by passivating the surface or by trapping the molecules inside surface immobilized lipid vesicles. Finally, we discuss recent examples where these methods were applied to study the dynamics of important cellular processes at the single-molecule level.
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Affiliation(s)
- Rajan Lamichhane
- Department of Chemistry, Wayne State University, Detroit MI 48202
| | - Amanda Solem
- Department of Chemistry, Wayne State University, Detroit MI 48202
| | - Will Black
- Department of Chemistry, Wayne State University, Detroit MI 48202
| | - David Rueda
- Department of Chemistry, Wayne State University, Detroit MI 48202
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19
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de Silva C, Walter NG. Leakage and slow allostery limit performance of single drug-sensing aptazyme molecules based on the hammerhead ribozyme. RNA (NEW YORK, N.Y.) 2009; 15:76-84. [PMID: 19029309 PMCID: PMC2612772 DOI: 10.1261/rna.1346609] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/02/2008] [Accepted: 10/13/2008] [Indexed: 05/27/2023]
Abstract
Engineered "aptazymes" fuse in vitro selected aptamers with ribozymes to create allosteric enzymes as biosensing components and artificial gene regulatory switches through ligand-induced conformational rearrangement and activation. By contrast, activating ligand is employed as an enzymatic cofactor in the only known natural aptazyme, the glmS ribozyme, which is devoid of any detectable conformational rearrangements. To better understand this difference in biosensing strategy, we monitored by single molecule fluorescence resonance energy transfer (FRET) and 2-aminopurine (AP) fluorescence the global conformational dynamics and local base (un)stacking, respectively, of a prototypical drug-sensing aptazyme, built from a theophylline aptamer and the hammerhead ribozyme. Single molecule FRET reveals that a catalytically active state with distal Stems I and III of the hammerhead ribozyme is accessed both in the theophylline-bound and, if less frequently, in the ligand-free state. The resultant residual activity (leakage) in the absence of theophylline contributes to a limited dynamic range of the aptazyme. In addition, site-specific AP labeling shows that rapid local theophylline binding to the aptamer domain leads to only slow allosteric signal transduction into the ribozyme core. Our findings allow us to rationalize the suboptimal biosensing performance of the engineered compared to the natural aptazyme and to suggest improvement strategies. Our single molecule FRET approach also monitors in real time the previously elusive equilibrium docking dynamics of the hammerhead ribozyme between several inactive conformations and the active, long-lived, Y-shaped conformer.
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Affiliation(s)
- Chamaree de Silva
- Biophysics, University of Michigan, Ann Arbor, Michigan 48109-1055, USA
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20
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Pereira MJB, Nikolova EN, Hiley SL, Jaikaran D, Collins RA, Walter NG. Single VS ribozyme molecules reveal dynamic and hierarchical folding toward catalysis. J Mol Biol 2008; 382:496-509. [PMID: 18656481 DOI: 10.1016/j.jmb.2008.07.020] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2008] [Revised: 07/01/2008] [Accepted: 07/08/2008] [Indexed: 01/18/2023]
Abstract
Non-coding RNAs of complex tertiary structure are involved in numerous aspects of the replication and processing of genetic information in many organisms; however, an understanding of the complex relationship between their structural dynamics and function is only slowly emerging. The Neurospora Varkud Satellite (VS) ribozyme provides a model system to address this relationship. First, it adopts a tertiary structure assembled from common elements, a kissing loop and two three-way junctions. Second, catalytic activity of the ribozyme is essential for replication of VS RNA in vivo and can be readily assayed in vitro. Here we exploit single molecule FRET to show that the VS ribozyme exhibits previously unobserved dynamic and heterogeneous hierarchical folding into an active structure. Readily reversible kissing loop formation combined with slow cleavage of the upstream substrate helix suggests a model whereby the structural dynamics of the VS ribozyme favor cleavage of the substrate downstream of the ribozyme core instead. This preference is expected to facilitate processing of the multimeric RNA replication intermediate into circular VS RNA, which is the predominant form observed in vivo.
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Affiliation(s)
- Miguel J B Pereira
- Department of Chemistry, Single Molecule Analysis Group, 930 N. University Ave., University of Michigan, Ann Arbor, MI 48109-1055, USA
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21
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Walter NG, Huang CY, Manzo AJ, Sobhy MA. Do-it-yourself guide: how to use the modern single-molecule toolkit. Nat Methods 2008; 5:475-89. [PMID: 18511916 PMCID: PMC2574008 DOI: 10.1038/nmeth.1215] [Citation(s) in RCA: 272] [Impact Index Per Article: 17.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Single-molecule microscopy has evolved into the ultimate-sensitivity toolkit to study systems from small molecules to living cells, with the prospect of revolutionizing the modern biosciences. Here we survey the current state of the art in single-molecule tools including fluorescence spectroscopy, tethered particle microscopy, optical and magnetic tweezers, and atomic force microscopy. We also provide guidelines for choosing the right approach from the available single-molecule toolkit for applications as diverse as structural biology, enzymology, nanotechnology and systems biology.
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Affiliation(s)
- Nils G Walter
- Department of Chemistry, Single Molecule Analysis Group, University of Michigan, 930 North University Avenue, Ann Arbor, Michigan 48109, USA.
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22
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Vilfan ID, Kamping W, van den Hout M, Candelli A, Hage S, Dekker NH. An RNA toolbox for single-molecule force spectroscopy studies. Nucleic Acids Res 2007; 35:6625-39. [PMID: 17905817 PMCID: PMC2095808 DOI: 10.1093/nar/gkm585] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2007] [Revised: 07/15/2007] [Accepted: 07/17/2007] [Indexed: 01/29/2023] Open
Abstract
Precise, controllable single-molecule force spectroscopy studies of RNA and RNA-dependent processes have recently shed new light on the dynamics and pathways of RNA folding and RNA-enzyme interactions. A crucial component of this research is the design and assembly of an appropriate RNA construct. Such a construct is typically subject to several criteria. First, single-molecule force spectroscopy techniques often require an RNA construct that is longer than the RNA molecules used for bulk biochemical studies. Next, the incorporation of modified nucleotides into the RNA construct is required for its surface immobilization. In addition, RNA constructs for single-molecule studies are commonly assembled from different single-stranded RNA molecules, demanding good control of hybridization or ligation. Finally, precautions to prevent RNase- and divalent cation-dependent RNA digestion must be taken. The rather limited selection of molecular biology tools adapted to the manipulation of RNA molecules, as well as the sensitivity of RNA to degradation, make RNA construct preparation a challenging task. We briefly illustrate the types of single-molecule force spectroscopy experiments that can be performed on RNA, and then present an overview of the toolkit of molecular biology techniques at one's disposal for the assembly of such RNA constructs. Within this context, we evaluate the molecular biology protocols in terms of their effectiveness in producing long and stable RNA constructs.
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Affiliation(s)
| | | | | | | | | | - Nynke H. Dekker
- Kavli Institute of Nanoscience, Faculty of Applied Sciences, Delft University of Technology, 2628 CJ Delft, The Netherlands
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23
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Lehmann J, Reichel A, Buguin A, Libchaber A. Efficiency of a self-aminoacylating ribozyme: effect of the length and base-composition of its 3' extension. RNA (NEW YORK, N.Y.) 2007; 13:1191-7. [PMID: 17556712 PMCID: PMC1924886 DOI: 10.1261/rna.500907] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/07/2023]
Abstract
Variants of a previously described small self-aminoacylating ribozyme are tested in order to uncover the potentialities of a 3' extension responsible for the esterification. The base-composition and the length of this specific part of the ribozyme are investigated. Very short extensions can still reach the active site, reflecting the small persistence length of RNA. The yield of aminoacylation is particularly high for ribozymes with extensions made up of a poly-U, for which a maximum of efficiency is observed for a total length of about 10 nucleotides. A simple model describing the behavior of this region of the ribozyme can account for the data.
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Affiliation(s)
- Jean Lehmann
- Center for Studies in Physics and Biology, The Rockefeller University, New York, NY, 10021, USA.
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24
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Mamasakhlisov YS, Hayryan S, Morozov VF, Hu CK. RNA folding in the presence of counterions. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2007; 75:061907. [PMID: 17677300 DOI: 10.1103/physreve.75.061907] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/29/2006] [Revised: 03/01/2007] [Indexed: 05/16/2023]
Abstract
We present a general thermodynamic picture of the folding of RNA-like heteropolymer based on the basic physical principles. The Hamiltonian of the model includes all characteristic interactions explicitly. A particular attention is paid to the electrostatic interactions whose role in the RNA folding is known to be crucial. In this paper we study RNA folding with the full Hamiltonian and describe the spin-glass behavior on the level of tertiary structure. We show that formation of the stable tertiary structure is possible in the random RNA-like molecule. By including into the model the nonspecific interactions of the RNA molecule with counterions, we derive the logarithmic dependencies of the melting and freezing temperatures on the ion concentration, which is consistent with experimental data [R. Shiman and D. E. Draper, J. Mol. Biol. 302, 79 (2000)]. We also infer that the large RNA folds slower than the hierarchical model predicts, which was observed in the experiments.
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25
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Walter NG, Meiners JC, Meyhofer E, Neubig RR, Sunahara RK, Perkins NC, Steel DG, Swanson JA. Under the microscope: single molecule symposium at the University of Michigan, 2006. Biopolymers 2007; 85:106-14. [PMID: 17080420 DOI: 10.1002/bip.20621] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
In recent years, a revolution has occurred in the basic sciences, which exploits novel single molecule detection and manipulation tools to track and analyze biopolymers in unprecedented detail. A recent Gordon Research Conference style meeting, hosted by the University of Michigan, highlighted current status and future perspectives of this rising field as researchers begin to integrate it with mainstream biology and nanotechnology.
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Affiliation(s)
- Nils G Walter
- Department of Chemistry, University of Michigan, 930 N. University Avenue, Ann Arbor, MI 48109-1055, USA.
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26
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Abstract
A recently developed tightly bound ion model can account for the correlation and fluctuation (i.e., different binding modes) of bound ions. However, the model cannot treat mixed ion solutions, which are physiologically relevant and biologically significant, and the model was based on B-DNA helices and thus cannot directly treat RNA helices. In the present study, we investigate the effects of ion correlation and fluctuation on the thermodynamic stability of finite length RNA helices immersed in a mixed solution of monovalent and divalent ions. Experimental comparisons demonstrate that the model gives improved predictions over the Poisson-Boltzmann theory, which has been found to underestimate the roles of multivalent ions such as Mg2+ in stabilizing DNA and RNA helices. The tightly bound ion model makes quantitative predictions on how the Na+-Mg2+ competition determines helix stability and its helix length-dependence. In addition, the model gives empirical formulas for the thermodynamic parameters as functions of Na+/Mg2+ concentrations and helix length. Such formulas can be quite useful for practical applications.
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Affiliation(s)
- Zhi-Jie Tan
- Department of Physics and Astronomy and Department of Biochemistry, University of Missouri, Columbia, Missouri 65211, USA
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