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Bukina V, Božič A. Context-dependent structure formation of hairpin motifs in bacteriophage MS2 genomic RNA. Biophys J 2024:S0006-3495(24)00526-5. [PMID: 39118324 DOI: 10.1016/j.bpj.2024.08.004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2024] [Revised: 07/17/2024] [Accepted: 08/05/2024] [Indexed: 08/10/2024] Open
Abstract
Many functions of ribonucleic acid (RNA) rely on its ability to assume specific sequence-structure motifs. Packaging signals found in certain RNA viruses are one such prominent example of functional RNA motifs. These signals are short hairpin loops that interact with coat proteins and drive viral self-assembly. As they are found in different positions along the much longer genomic RNA, the formation of their correct structure occurs as a part of a larger context. Any changes to this context can consequently lead to changes in the structure of the motifs themselves. In fact, previous studies have shown that structure and function of RNA motifs can be highly context sensitive to the flanking sequence surrounding them. However, in what ways different flanking sequences influence the structure of an RNA motif they surround has yet to be studied in detail. We focus on a hairpin-rich region of the RNA genome of bacteriophage MS2-a well-studied RNA virus with a wide potential for use in biotechnology-and systematically examine context-dependent structural stability of 14 previously identified hairpin motifs, which include putative and confirmed packaging signals. Combining secondary and tertiary RNA structure prediction of the hairpin motifs placed in different contexts, ranging from the native genomic sequence to random RNA sequences and unstructured poly-U sequences, we determine different measures of motif structural stability. In this way, we show that while some motif structures can be stable in any context, others require specific context provided by the genome. Our results demonstrate the importance of context in RNA structure formation and how changes in the flanking sequence of an RNA motif sometimes lead to drastic changes in its structure. Structural stability of a motif in different contexts could provide additional insights into its functionality as well as assist in determining whether it remains functional when intentionally placed in other contexts.
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Affiliation(s)
- Veronika Bukina
- Department of Theoretical Physics, Jožef Stefan Institute, Ljubljana, Slovenia; Department of Physics, Faculty of Mathematics and Physics, University of Ljubljana, Ljubljana, Slovenia
| | - Anže Božič
- Department of Theoretical Physics, Jožef Stefan Institute, Ljubljana, Slovenia.
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2
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Keshavarz-Joud P, Zhao L, Bobe D, Hernandez C, Kopylov M, Yen LY, Djeddar N, Thompson B, Connors C, Gibson G, Bryksin A, Finn M. Exploring the Landscape of the PP7 Virus-like Particle for Peptide Display. ACS NANO 2023; 17:18470-18480. [PMID: 37669408 PMCID: PMC10540251 DOI: 10.1021/acsnano.3c06178] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/06/2023] [Accepted: 08/29/2023] [Indexed: 09/07/2023]
Abstract
Self-assembling virus-like particles (VLPs) can tolerate a wide degree of genetic and chemical manipulation to their capsid protein to display a foreign molecule polyvalently. We previously reported the successful incorporation of foreign peptide sequences in the junction loop and onto the C-terminus of PP7 dimer VLPs, as these regions are accessible for surface display on assembled capsids. Here, we report the implementation of a library-based approach to test the assembly tolerance of PP7 dimer capsid proteins to insertions or terminal extensions of randomized 15-mer peptide sequences. By performing two iterative rounds of assembly-based selection, we evaluated the degree of favorability of all 20 amino acids at each of the 15 randomized positions. Deep sequencing analysis revealed a distinct preference for the inclusion of hydrophilic peptides and negatively charged amino acids (Asp and Glu) and the exclusion of positively charged peptides and bulky and hydrophobic amino acid residues (Trp, Phe, Tyr, and Cys). Within the libraries tested here, we identified 4000 to 22,000 unique 15-mer peptide sequences that can successfully be displayed on the surface of the PP7 dimer capsid. Overall, the use of small initial libraries consisting of no more than a few million members yielded a significantly larger number of unique and assembly-competent VLP sequences than have been previously characterized for this class of nucleoprotein particle.
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Affiliation(s)
- Parisa Keshavarz-Joud
- School
of Chemistry and Biochemistry, Georgia Institute
of Technology, Atlanta, Georgia 30306, United States
| | - Liangjun Zhao
- School
of Chemistry and Biochemistry, Georgia Institute
of Technology, Atlanta, Georgia 30306, United States
| | - Daija Bobe
- New
York Structural Biology Center, New York, New York 10027, United States
| | - Carolina Hernandez
- New
York Structural Biology Center, New York, New York 10027, United States
| | - Mykhailo Kopylov
- New
York Structural Biology Center, New York, New York 10027, United States
| | - Laura Y. Yen
- New
York Structural Biology Center, New York, New York 10027, United States
| | - Naima Djeddar
- Parker
H. Petit Institute for Bioengineering and Biosciences, Georgia Institute of Technology, Atlanta, Georgia 30306, United States
| | - Brianna Thompson
- School
of Chemistry and Biochemistry, Georgia Institute
of Technology, Atlanta, Georgia 30306, United States
| | - Caleb Connors
- School
of Biological Sciences, Georgia Institute
of Technology, Atlanta, Georgia 30306, United States
| | - Greg Gibson
- School
of Biological Sciences, Georgia Institute
of Technology, Atlanta, Georgia 30306, United States
| | - Anton Bryksin
- Parker
H. Petit Institute for Bioengineering and Biosciences, Georgia Institute of Technology, Atlanta, Georgia 30306, United States
| | - M.G. Finn
- School
of Chemistry and Biochemistry, Georgia Institute
of Technology, Atlanta, Georgia 30306, United States
- School
of Biological Sciences, Georgia Institute
of Technology, Atlanta, Georgia 30306, United States
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3
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Lalwani Prakash D, Gosavi S. Understanding the Folding Mediated Assembly of the Bacteriophage MS2 Coat Protein Dimers. J Phys Chem B 2021; 125:8722-8732. [PMID: 34339197 DOI: 10.1021/acs.jpcb.1c03928] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The capsids of RNA viruses such as MS2 are great models for studying protein self-assembly because they are made almost entirely of multiple copies of a single coat protein (CP). Although CP is the minimal repeating unit of the capsid, previous studies have shown that CP exists as a homodimer (CP2) even in an acid-disassembled system, indicating that CP2 is an obligate dimer. Here, we investigate the molecular basis of this obligate dimerization using coarse-grained structure-based models and molecular dynamics simulations. We find that, unlike monomeric proteins of similar size, CP populates a single partially folded ensemble whose "foldedness" is sensitive to denaturing conditions. In contrast, CP2 folds similarly to single-domain proteins populating only the folded and the unfolded ensembles, separated by a prominent folding free energy barrier. Several intramonomer contacts form early, but the CP2 folding barrier is crossed only when the intermonomer contacts are made. A dissection of the structure of CP2 through mutant folding simulations shows that the folding barrier arises both from the topology of CP and the interface contacts of CP2. Together, our results show that CP2 is an obligate dimer because of kinetic stability, that is, dimerization induces a folding barrier and that makes it difficult for proteins in the dimer minimum to partially unfold and access the monomeric state without completely unfolding. We discuss the advantages of this obligate dimerization in the context of dimer design and virus stability.
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Affiliation(s)
- Digvijay Lalwani Prakash
- Simons Centre for the Study of Living Machines, National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bengaluru 560065, India
| | - Shachi Gosavi
- Simons Centre for the Study of Living Machines, National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bengaluru 560065, India
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Ahmed F, Sharma M, Al-Ghamdi AA, Al-Yami SM, Al-Salami AM, Refai MY, Warsi MK, Howladar SM, Baeshen MN. A Comprehensive Analysis of cis-Acting RNA Elements in the SARS-CoV-2 Genome by a Bioinformatics Approach. Front Genet 2020; 11:572702. [PMID: 33424918 PMCID: PMC7786107 DOI: 10.3389/fgene.2020.572702] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2020] [Accepted: 10/14/2020] [Indexed: 01/08/2023] Open
Abstract
The emergence of a new coronavirus (CoV), severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), responsible for severe respiratory disease in humans termed coronavirus disease of 2019 (COVID-19), became a new global threat for health and the economy. The SARS-CoV-2 genome is about a 29,800-nucleotide-long plus-strand RNA that can form functionally important secondary and higher-order structures called cis-acting RNA elements. These elements can interact with viral proteins, host proteins, or other RNAs and be involved in regulating translation and replication processes of the viral genome and encapsidation of the virus. However, the cis-acting RNA elements and their biological roles in SARS-CoV-2 as well as their comparative analysis in the closely related viral genome have not been well explored, which is very important to understand the molecular mechanism of viral infection and pathogenies. In this study, we used a bioinformatics approach to identify the cis-acting RNA elements in the SARS-CoV-2 genome. Initially, we aligned the full genomic sequence of six different CoVs, and a phylogenetic analysis was performed to understand their evolutionary relationship. Next, we predicted the cis-acting RNA elements in the SARS-CoV-2 genome using the structRNAfinder tool. Then, we annotated the location of these cis-acting RNA elements in different genomic regions of SARS-CoV-2. After that, we analyzed the sequence conservation patterns of each cis-acting RNA element among the six CoVs. Finally, the presence of cis-acting RNA elements across different CoV genomes and their comparative analysis was performed. Our study identified 12 important cis-acting RNA elements in the SARS-CoV-2 genome; among them, Corona_FSE, Corona_pk3, and s2m are highly conserved across most of the studied CoVs, and Thr_leader, MAT2A_D, and MS2 are uniquely present in SARS-CoV-2. These RNA structure elements can be involved in viral translation, replication, and encapsidation and, therefore, can be potential targets for better treatment of COVID-19. It is imperative to further characterize these cis-acting RNA elements experimentally for a better mechanistic understanding of SARS-CoV-2 infection and therapeutic intervention.
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Affiliation(s)
- Firoz Ahmed
- Department of Biochemistry, College of Science, University of Jeddah, Jeddah, Saudi Arabia
- University of Jeddah Center for Scientific and Medical Research, University of Jeddah, Jeddah, Saudi Arabia
| | - Monika Sharma
- Department of Chemical Sciences, Indian Institute of Science Education and Research, Mohali, India
| | | | | | | | - Mohammed Y. Refai
- Department of Biochemistry, College of Science, University of Jeddah, Jeddah, Saudi Arabia
- University of Jeddah Center for Scientific and Medical Research, University of Jeddah, Jeddah, Saudi Arabia
| | - Mohiuddin Khan Warsi
- Department of Biochemistry, College of Science, University of Jeddah, Jeddah, Saudi Arabia
- University of Jeddah Center for Scientific and Medical Research, University of Jeddah, Jeddah, Saudi Arabia
| | - Saad M. Howladar
- Department of Biology, College of Science, University of Jeddah, Jeddah, Saudi Arabia
| | - Mohammed N. Baeshen
- Department of Biology, College of Science, University of Jeddah, Jeddah, Saudi Arabia
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Abstract
ssRNA phages belonging to the family Leviviridae are among the tiniest viruses, infecting various Gram-negative bacteria by adsorption to their pilus structures. Due to their simplicity, they have been intensively studied as models for understanding various problems in molecular biology and virology. Several of the studied ssRNA characteristics, such as coat protein–RNA interactions and the ability to readily form virus-like particles in recombinant expression systems, have fueled many practical applications such as RNA labeling and tracking systems and vaccine development. In this chapter, we review the life cycle, structure and applications of these small yet fascinating viruses.
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Gorzelnik KV, Cui Z, Reed CA, Jakana J, Young R, Zhang J. Asymmetric cryo-EM structure of the canonical Allolevivirus Qβ reveals a single maturation protein and the genomic ssRNA in situ. Proc Natl Acad Sci U S A 2016; 113:11519-11524. [PMID: 27671640 PMCID: PMC5068298 DOI: 10.1073/pnas.1609482113] [Citation(s) in RCA: 57] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Single-stranded (ss) RNA viruses infect all domains of life. To date, for most ssRNA virions, only the structures of the capsids and their associated protein components have been resolved to high resolution. Qβ, an ssRNA phage specific for the conjugative F-pilus, has a T = 3 icosahedral lattice of coat proteins assembled around its 4,217 nucleotides of genomic RNA (gRNA). In the mature virion, the maturation protein, A2, binds to the gRNA and is required for adsorption to the F-pilus. Here, we report the cryo-electron microscopy (cryo-EM) structures of Qβ with and without symmetry applied. The icosahedral structure, at 3.7-Å resolution, resolves loops not previously seen in the published X-ray structure, whereas the asymmetric structure, at 7-Å resolution, reveals A2 and the gRNA. A2 contains a bundle of α-helices and replaces one dimer of coat proteins at a twofold axis. The helix bundle binds gRNA, causing denser packing of RNA in its proximity, which asymmetrically expands the surrounding coat protein shell to potentially facilitate RNA release during infection. We observe a fixed pattern of gRNA organization among all viral particles, with the major and minor grooves of RNA helices clearly visible. A single layer of RNA directly contacts every copy of the coat protein, with one-third of the interactions occurring at operator-like RNA hairpins. These RNA-coat interactions stabilize the tertiary structure of gRNA within the virion, which could further provide a roadmap for capsid assembly.
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Affiliation(s)
- Karl V Gorzelnik
- Center for Phage Technology, Department of Biochemistry and Biophysics, Texas A&M University, College Station, TX 77843
| | - Zhicheng Cui
- Center for Phage Technology, Department of Biochemistry and Biophysics, Texas A&M University, College Station, TX 77843
| | - Catrina A Reed
- Center for Phage Technology, Department of Biochemistry and Biophysics, Texas A&M University, College Station, TX 77843
| | - Joanita Jakana
- National Center for Macromolecular Imaging, Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, TX 77030
| | - Ry Young
- Center for Phage Technology, Department of Biochemistry and Biophysics, Texas A&M University, College Station, TX 77843
| | - Junjie Zhang
- Center for Phage Technology, Department of Biochemistry and Biophysics, Texas A&M University, College Station, TX 77843;
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Rolfsson Ó, Middleton S, Manfield IW, White SJ, Fan B, Vaughan R, Ranson NA, Dykeman E, Twarock R, Ford J, Kao CC, Stockley PG. Direct Evidence for Packaging Signal-Mediated Assembly of Bacteriophage MS2. J Mol Biol 2016; 428:431-48. [PMID: 26608810 PMCID: PMC4751978 DOI: 10.1016/j.jmb.2015.11.014] [Citation(s) in RCA: 71] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2015] [Revised: 11/06/2015] [Accepted: 11/08/2015] [Indexed: 01/20/2023]
Abstract
Using cross-linking coupled to matrix-assisted laser desorption/ionization mass spectrometry and CLIP-Seq sequencing, we determined the peptide and oligonucleotide sequences at the interfaces between the capsid proteins and the genomic RNA of bacteriophage MS2. The results suggest that the same coat protein (CP)-RNA and maturation protein (MP)-RNA interfaces are used in every viral particle. The portions of the viral RNA in contact with CP subunits span the genome, consistent with a large number of discrete and similar contacts within each particle. Many of these sites match previous predictions of the locations of multiple, dispersed and degenerate RNA sites with cognate CP affinity termed packaging signals (PSs). Chemical RNA footprinting was used to compare the secondary structures of protein-free genomic fragments and the RNA in the virion. Some PSs are partially present in protein-free RNA but others would need to refold from their dominant solution conformations to form the contacts identified in the virion. The RNA-binding peptides within the MP map to two sections of the N-terminal half of the protein. Comparison of MP sequences from related phages suggests a similar arrangement of RNA-binding sites, although these N-terminal regions have only limited sequence conservation. In contrast, the sequences of the C-termini are highly conserved, consistent with them encompassing pilin-binding domains required for initial contact with host cells. These results provide independent and unambiguous support for the assembly of MS2 virions via a PS-mediated mechanism involving a series of induced-fit viral protein interactions with RNA.
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Affiliation(s)
- Óttar Rolfsson
- Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds LS2 9JT, United Kingdom
| | - Stefani Middleton
- Department of Molecular and Cellular Biochemistry, Indiana University, Bloomington, IN 47405, USA; The Center for Genomics and Bioinformatics, Indiana University, Bloomington, IN 47405, USA
| | - Iain W Manfield
- Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds LS2 9JT, United Kingdom
| | - Simon J White
- Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds LS2 9JT, United Kingdom
| | - Baochang Fan
- Department of Molecular and Cellular Biochemistry, Indiana University, Bloomington, IN 47405, USA
| | - Robert Vaughan
- Department of Molecular and Cellular Biochemistry, Indiana University, Bloomington, IN 47405, USA
| | - Neil A Ranson
- Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds LS2 9JT, United Kingdom
| | - Eric Dykeman
- Department of Biology and Mathematics and York Centre for Complex Systems Analysis, University of York, York YO10 5DD, United Kingdom
| | - Reidun Twarock
- Department of Biology and Mathematics and York Centre for Complex Systems Analysis, University of York, York YO10 5DD, United Kingdom
| | - James Ford
- The Center for Genomics and Bioinformatics, Indiana University, Bloomington, IN 47405, USA
| | - C Cheng Kao
- Department of Molecular and Cellular Biochemistry, Indiana University, Bloomington, IN 47405, USA
| | - Peter G Stockley
- Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds LS2 9JT, United Kingdom
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8
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The Role of Packaging Sites in Efficient and Specific Virus Assembly. J Mol Biol 2015; 427:2451-2467. [PMID: 25986309 DOI: 10.1016/j.jmb.2015.05.008] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2015] [Revised: 04/21/2015] [Accepted: 05/10/2015] [Indexed: 12/25/2022]
Abstract
During the life cycle of many single-stranded RNA viruses, including many human pathogens, a protein shell called the capsid spontaneously assembles around the viral genome. Understanding the mechanisms by which capsid proteins selectively assemble around the viral RNA amidst diverse host RNAs is a key question in virology. In one proposed mechanism, short sequences (packaging sites) within the genomic RNA promote rapid and efficient assembly through specific interactions with the capsid proteins. In this work, we develop a coarse-grained particle-based computational model for capsid proteins and RNA that represents protein-RNA interactions arising both from nonspecific electrostatics and from specific packaging site interactions. Using Brownian dynamics simulations, we explore how the efficiency and specificity of assembly depend on solution conditions (which control protein-protein and nonspecific protein-RNA interactions) and the strength and number of packaging sites. We identify distinct regions in parameter space in which packaging sites lead to highly specific assembly via different mechanisms and others in which packaging sites lead to kinetic traps. We relate these computational predictions to in vitro assays for specificity in which cognate viral RNAs compete against non-cognate RNAs for assembly by capsid proteins.
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Solving a Levinthal's paradox for virus assembly identifies a unique antiviral strategy. Proc Natl Acad Sci U S A 2014; 111:5361-6. [PMID: 24706827 DOI: 10.1073/pnas.1319479111] [Citation(s) in RCA: 93] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
One of the important puzzles in virology is how viruses assemble the protein containers that package their genomes rapidly and efficiently in vivo while avoiding triggering their hosts' antiviral defenses. Viral assembly appears directed toward a relatively small subset of the vast number of all possible assembly intermediates and pathways, akin to Levinthal's paradox for the folding of polypeptide chains. Using an in silico assembly model, we demonstrate that this reduction in complexity can be understood if aspects of in vivo assembly, which have mostly been neglected in in vitro experimental and theoretical modeling assembly studies, are included in the analysis. In particular, we show that the increasing viral coat protein concentration that occurs in infected cells plays unexpected and vital roles in avoiding potential kinetic assembly traps, significantly reducing the number of assembly pathways and assembly initiation sites, and resulting in enhanced assembly efficiency and genome packaging specificity. Because capsid assembly is a vital determinant of the overall fitness of a virus in the infection process, these insights have important consequences for our understanding of how selection impacts on the evolution of viral quasispecies. These results moreover suggest strategies for optimizing the production of protein nanocontainers for drug delivery and of virus-like particles for vaccination. We demonstrate here in silico that drugs targeting the specific RNA-capsid protein contacts can delay assembly, reduce viral load, and lead to an increase of misencapsidation of cellular RNAs, hence opening up unique avenues for antiviral therapy.
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10
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Stockley PG, Ranson NA, Twarock R. A new paradigm for the roles of the genome in ssRNA viruses. Future Virol 2013. [DOI: 10.2217/fvl.12.84] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Recent work with RNA phages and an ssRNA plant satellite virus challenges the widely held view that the sequences and structures of genomic RNAs are unimportant for virion assembly. In the T=3 phages, RNA–coat protein interactions occur throughout the genome, defining the quasiconformers of their protein shells. In the plant virus, there are multiple packaging signals dispersed throughout the genome that overcome electrostatic barriers to protein self-assembly. Both viral coat proteins cause the solution structures of their cognate genomes to collapse into a form that is readily encapsidated in a two-stage assembly process. Such similar behavior in two structurally unrelated viral protein folds implies that this might be a conserved feature of many viral assembly reactions. These results suggest a highly defined structure for the RNA in the virions, consistent with recent structural studies. They also have implications both for subsequent genome release during infection and for the evolution of viral sequences.
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Affiliation(s)
- Peter G Stockley
- Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, LS2 9JT, UK.
| | - Neil A Ranson
- Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, LS2 9JT, UK
| | - Reidun Twarock
- Departments of Biology & Mathematics, York Centre for Complex Systems Analysis, University of York, York, YO10 5DD, UK
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11
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Fiedler JD, Higginson C, Hovlid ML, Kislukhin AA, Castillejos A, Manzenrieder F, Campbell MG, Voss NR, Potter CS, Carragher B, Finn M. Engineered mutations change the structure and stability of a virus-like particle. Biomacromolecules 2012; 13:2339-48. [PMID: 22830650 PMCID: PMC3432585 DOI: 10.1021/bm300590x] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
The single-coat protein (CP) of bacteriophage Qβ self-assembles into T = 3 icosahedral virus-like particles (VLPs), of interest for a wide range of applications. These VLPs are very stable, but identification of the specific molecular determinants of this stability is lacking. To investigate these determinants along with manipulations that confer more capabilities to our VLP material, we manipulated the CP primary structure to test the importance of various putative stabilizing interactions. Optimization of a procedure to incorporate fused CP subunits allowed for good control over the average number of covalent dimers in each VLP. We confirmed that the disulfide linkages are the most important stabilizing elements for the capsid and that acidic conditions significantly enhance the resistance of VLPs to thermal degradation. Interdimer interactions were found to be less important for VLP assembly than intradimer interactions. Finally, a single point mutation in the CP resulted in a population of smaller VLPs in three distinct structural forms.
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Affiliation(s)
- Jason D. Fiedler
- Department of Chemistry, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, California 92037, USA
| | - Cody Higginson
- Department of Chemistry, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, California 92037, USA
| | - Marisa L. Hovlid
- Department of Chemistry, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, California 92037, USA
| | - Alexander A. Kislukhin
- Department of Chemistry, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, California 92037, USA
| | - Alexandra Castillejos
- Department of Chemistry, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, California 92037, USA
| | - Florian Manzenrieder
- Department of Chemistry, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, California 92037, USA
| | - Melody G. Campbell
- Department of Cell Biology and the National Resource for Automated Molecular Spectroscopy, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, California 92037, USA
| | - Neil R. Voss
- Department of Cell Biology and the National Resource for Automated Molecular Spectroscopy, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, California 92037, USA
| | - Clinton S. Potter
- Department of Cell Biology and the National Resource for Automated Molecular Spectroscopy, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, California 92037, USA
| | - Bridget Carragher
- Department of Cell Biology and the National Resource for Automated Molecular Spectroscopy, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, California 92037, USA
| | - M.G. Finn
- Department of Chemistry, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, California 92037, USA
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12
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García-Villada L, Drake JW. The three faces of riboviral spontaneous mutation: spectrum, mode of genome replication, and mutation rate. PLoS Genet 2012; 8:e1002832. [PMID: 22844250 PMCID: PMC3405988 DOI: 10.1371/journal.pgen.1002832] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2012] [Accepted: 05/31/2012] [Indexed: 11/19/2022] Open
Abstract
Riboviruses (RNA viruses without DNA replication intermediates) are the most abundant pathogens infecting animals and plants. Only a few riboviral infections can be controlled with antiviral drugs, mainly because of the rapid appearance of resistance mutations. Little reliable information is available concerning i) kinds and relative frequencies of mutations (the mutational spectrum), ii) mode of genome replication and mutation accumulation, and iii) rates of spontaneous mutation. To illuminate these issues, we developed a model in vivo system based on phage Qß infecting its natural host, Escherichia coli. The Qß RT gene encoding the Read-Through protein was used as a mutation reporter. To reduce uncertainties in mutation frequencies due to selection, the experimental Qß populations were established after a single cycle of infection and selection against RT− mutants during phage growth was ameliorated by plasmid-based RT complementation in trans. The dynamics of Qß genome replication were confirmed to reflect the linear process of iterative copying (the stamping-machine mode). A total of 32 RT mutants were detected among 7,517 Qß isolates. Sequencing analysis of 45 RT mutations revealed a spectrum dominated by 39 transitions, plus 4 transversions and 2 indels. A clear template•primer mismatch bias was observed: A•C>C•A>U•G>G•U> transversion mismatches. The average mutation rate per base replication was ≈9.1×10−6 for base substitutions and ≈2.3×10−7 for indels. The estimated mutation rate per genome replication, μg, was ≈0.04 (or, per phage generation, ≈0.08), although secondary RT mutations arose during the growth of some RT mutants at a rate about 7-fold higher, signaling the possible impact of transitory bouts of hypermutation. These results are contrasted with those previously reported for other riboviruses to depict the current state of the art in riboviral mutagenesis. Viral disease is a subject of major concern in public health. Diseases produced by riboviruses (RNA viruses sensu stricto) represent a special urgency, because these viruses display an exceptional capability to generate resistance mutations against antiviral drugs. Unfortunately, little is known about the rate and nature of spontaneous mutation in riboviruses. Thus, characterization of their mutation process may be helpful in the development of improved ways to counteract riboviral diseases. In this study, we investigated the mutation process in vivo of a model ribovirus, the bacteriophage Qß, focusing on three key aspects: i) the kinds and relative frequencies of mutations, ii) the mode of genome replication, and iii) the rate of spontaneous mutation. Our results, combined with other information about riboviral mutagenesis, depict a ribovirus mutation spectrum largely dominated by transitions, a predominantly linear mode of genome replication, and a mutation rate per genome replication on the order of 0.04 for bacteriophages and plant viruses but perhaps an order of magnitude higher for mammalian riboviruses.
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Affiliation(s)
| | - John W. Drake
- Laboratory of Molecular Genetics, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina, United States of America
- * E-mail:
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13
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Toropova K, Stockley PG, Ranson NA. Visualising a viral RNA genome poised for release from its receptor complex. J Mol Biol 2011; 408:408-19. [PMID: 21376055 DOI: 10.1016/j.jmb.2011.02.040] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2010] [Revised: 02/11/2011] [Accepted: 02/15/2011] [Indexed: 02/05/2023]
Abstract
We describe the cryo-electron microscopy structure of bacteriophage MS2 bound to its receptor, the bacterial F-pilus. The virus contacts the pilus at a capsid 5-fold vertex, thus locating the surface-accessible portion of the single copy of the pilin-binding maturation protein present in virions. This arrangement allows a 5-fold averaged map to be calculated, showing for the first time in any virus-receptor complex the nonuniform distribution of RNA within the capsid. Strikingly, at the vertex that contacts the pilus, a rod of density that may include contributions from both genome and maturation protein sits above a channel that goes through the capsid to the outside. This density is reminiscent of the DNA density observed in the exit channel of double-stranded DNA phages, suggesting that the RNA-maturation protein complex is poised to leave the capsid as the first step of the infection process.
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Affiliation(s)
- Katerina Toropova
- Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, LS2 9JT, UK
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14
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Rolfsson Ó, Toropova K, Ranson NA, Stockley PG. Mutually-induced conformational switching of RNA and coat protein underpins efficient assembly of a viral capsid. J Mol Biol 2010; 401:309-322. [PMID: 20684044 PMCID: PMC4793595 DOI: 10.1016/j.jmb.2010.05.058] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Single-stranded RNA viruses package their genomes into capsids enclosing fixed volumes. We assayed the ability of bacteriophage MS2 coat protein to package large, defined fragments of its genomic, single-stranded RNA. We show that the efficiency of packaging into a T=3 capsid in vitro is inversely proportional to RNA length, implying that there is a free-energy barrier to be overcome during assembly. All the RNAs examined have greater solution persistence lengths than the internal diameter of the capsid into which they become packaged, suggesting that protein-mediated RNA compaction must occur during assembly. Binding ethidium bromide to one of these RNA fragments, which would be expected to reduce its flexibility, severely inhibited packaging, consistent with this idea. Cryo-EM structures of the capsids assembled in these experiments with the sub-genomic RNAs show a layer of RNA density beneath the coat protein shell but lack density for the inner RNA shell seen in the wild-type virion. The inner layer is restored when full-length virion RNA is used in the assembly reaction, implying that it becomes ordered only when the capsid is filled, presumably because of the effects of steric and/or electrostatic repulsions. The cryo-EM results explain the length dependence of packaging. In addition, they show that for the sub-genomic fragments the strongest ordered RNA density occurs below the coat protein dimers forming the icosahedral 5-fold axes of the capsid. There is little such density beneath the proteins at the 2-fold axes, consistent with our model in which coat protein dimers binding to RNA stem-loops located at sites throughout the genome leads to switching of their preferred conformations, thus regulating the placement of the quasi-conformers needed to build the T=3 capsid. The data are consistent with mutual chaperoning of both RNA and coat protein conformations, partially explaining the ability of such viruses to assemble so rapidly and accurately.
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Affiliation(s)
- Óttar Rolfsson
- Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, LS2 9JT, UK
| | - Katerina Toropova
- Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, LS2 9JT, UK
| | - Neil A. Ranson
- Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, LS2 9JT, UK
| | - Peter G. Stockley
- Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, LS2 9JT, UK
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15
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Basnak G, Morton VL, Rolfsson Ó, Stonehouse NJ, Ashcroft AE, Stockley PG. Viral genomic single-stranded RNA directs the pathway toward a T=3 capsid. J Mol Biol 2010; 395:924-36. [PMID: 19913556 PMCID: PMC4785722 DOI: 10.1016/j.jmb.2009.11.018] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2009] [Revised: 11/02/2009] [Accepted: 11/05/2009] [Indexed: 11/20/2022]
Abstract
The molecular mechanisms controlling genome packaging by single-stranded RNA viruses are still largely unknown. It is necessary in most cases for the protein to adopt different conformations at different positions on the capsid lattice in order to form a viral capsid from multiple copies of a single protein. We showed previously that such quasi-equivalent conformers of RNA bacteriophage MS2 coat protein dimers (CP(2)) can be switched by sequence-specific interaction with a short RNA stem-loop (TR) that occurs only once in the wild-type phage genome. In principle, multiple switching events are required to generate the phage T=3 capsid. We have therefore investigated the sequence dependency of this event using two RNA aptamer sequences selected to bind the phage coat protein and an analogous packaging signal from phage Qbeta known to be discriminated against by MS2 coat protein both in vivo and in vitro. All three non-cognate stem-loops support T=3 shell formation, but none shows the kinetic-trapping effect seen when TR is mixed with equimolar CP(2). We show that this reflects the fact that they are poor ligands compared with TR, failing to saturate the coat protein under the assay conditions, ensuring that sufficient amounts of both types of dimer required for efficient assembly are present in these reactions. Increasing the non-cognate RNA concentration restores the kinetic trap, confirming this interpretation. We have also assessed the effects of extending the TR stem-loop at the 5' or 3' end with short genomic sequences. These longer RNAs all show evidence of the kinetic trap, reflecting the fact that they all contain the TR sequence and are more efficient at promoting capsid formation than TR. Mass spectrometry has shown that at least two pathways toward the T=3 shell occur in TR-induced assembly reactions: one via formation of a 3-fold axis and another that creates an extended 5-fold complex. The longer genomic RNAs suppress the 5-fold pathway, presumably as a consequence of steric clashes between multiply bound RNAs. Reversing the orientation of the extension sequences with respect to the TR stem-loop produces RNAs that are poor assembly initiators. The data support the idea that RNA-induced protein conformer switching occurs throughout assembly of the T=3 shell and show that both positional and sequence-specific effects outside the TR stem-loop can have significant impacts on the precise assembly pathway followed.
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Affiliation(s)
- Gabriella Basnak
- Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds LS2 9JT, UK
| | - Victoria L. Morton
- Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds LS2 9JT, UK
| | - Óttar Rolfsson
- Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds LS2 9JT, UK
| | - Nicola J. Stonehouse
- Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds LS2 9JT, UK
| | - Alison E. Ashcroft
- Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds LS2 9JT, UK
| | - Peter G. Stockley
- Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds LS2 9JT, UK
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16
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Rumnieks J, Ose V, Tars K, Dislers A, Strods A, Cielens I, Renhofa R. Assembly of mixed rod-like and spherical particles from group I and II RNA bacteriophage coat proteins. Virology 2009; 391:187-94. [PMID: 19604532 DOI: 10.1016/j.virol.2009.06.023] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2009] [Revised: 03/25/2009] [Accepted: 06/13/2009] [Indexed: 10/20/2022]
Abstract
The capsids of single-stranded RNA bacteriophages show remarkable structural similarity. In an attempt to test whether the coat protein (CP) from one bacteriophage could substitute for the CP of another and form mixed particles, we reassembled capsids in vitro from a mixture of different RNA phage CP dimers together with E. coli ribosomal RNA. Surprisingly, mixing CPs from phages belonging to groups I and II led to appearance of rod-like particles along with icosahedral spherical capsids, both containing a mixture of the two CPs. Rods and mixed spherical capsids containing host RNA were also obtained in vivo in bacteria expressing simultaneously fr and GA CPs. In a co-infection of the two phages, however, only authentic fr and GA virions were formed. Coat protein mutants in the FG loop were unable to assemble into rods, suggesting that these loops are involved in the formation of the aberrant particles.
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Affiliation(s)
- Janis Rumnieks
- Latvian Biomedical Research and Study Centre, Department of Protein Engineering, Ratsupites 1, LV1067, Riga, Latvia.
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17
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Horn WT, Tars K, Grahn E, Helgstrand C, Baron AJ, Lago H, Adams CJ, Peabody DS, Phillips SE, Stonehouse NJ, Liljas L, Stockley PG. Structural basis of RNA binding discrimination between bacteriophages Qbeta and MS2. Structure 2006; 14:487-95. [PMID: 16531233 PMCID: PMC7612262 DOI: 10.1016/j.str.2005.12.006] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2005] [Revised: 12/13/2005] [Accepted: 12/14/2005] [Indexed: 01/07/2023]
Abstract
Sequence-specific interactions between RNA stem-loops and coat protein (CP) subunits play vital roles in the life cycles of the RNA bacteriophages, e.g., by allowing translational repression of their replicase cistrons and tagging their own RNA genomes for encapsidation. The CPs of bacteriophages Qbeta and MS2 each discriminate in favor of their cognate translational operators, even in the presence of closely related operators from other phages in vivo. Discrete mutations within the MS2 CP have been shown to relax this discrimination in vitro. We have determined the structures of eight complexes between such mutants and both MS2 and Qbeta stem-loops with X-ray crystallography. In conjunction with previously determined in vivo repression data, the structures enable us to propose the molecular basis for the discrimination mechanism.
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Affiliation(s)
- Wilf T. Horn
- Astbury Centre for Structural Molecular Biology University of Leeds Leeds LS2 9JT United Kingdom
| | - Kaspars Tars
- Department of Cell and Molecular Biology Uppsala University Box 596 SE-751 24 Uppsala Sweden
| | - Elin Grahn
- Department of Cell and Molecular Biology Uppsala University Box 596 SE-751 24 Uppsala Sweden
| | - Charlotte Helgstrand
- Department of Cell and Molecular Biology Uppsala University Box 596 SE-751 24 Uppsala Sweden
| | - Andrew J. Baron
- Astbury Centre for Structural Molecular Biology University of Leeds Leeds LS2 9JT United Kingdom
| | - Hugo Lago
- Astbury Centre for Structural Molecular Biology University of Leeds Leeds LS2 9JT United Kingdom
| | - Chris J. Adams
- Astbury Centre for Structural Molecular Biology University of Leeds Leeds LS2 9JT United Kingdom
| | - David S. Peabody
- Department of Molecular Genetics and Microbiology, and the Cancer Research and Treatment Center University of New Mexico School of Medicine Albuquerque, New Mexico 87131
| | - Simon E.V. Phillips
- Astbury Centre for Structural Molecular Biology University of Leeds Leeds LS2 9JT United Kingdom
| | - Nicola J. Stonehouse
- Astbury Centre for Structural Molecular Biology University of Leeds Leeds LS2 9JT United Kingdom
| | - Lars Liljas
- Department of Cell and Molecular Biology Uppsala University Box 596 SE-751 24 Uppsala Sweden
| | - Peter G. Stockley
- Astbury Centre for Structural Molecular Biology University of Leeds Leeds LS2 9JT United Kingdom
- Correspondence:
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18
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Bruinsma RF. Physics of RNA and viral assembly. THE EUROPEAN PHYSICAL JOURNAL. E, SOFT MATTER 2006; 19:303-10. [PMID: 16554977 DOI: 10.1140/epje/i2005-10071-1] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/11/2005] [Accepted: 02/04/2006] [Indexed: 05/07/2023]
Abstract
The overview discusses the application of physical arguments to structure and function of single-stranded viral RNA genomes.
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Affiliation(s)
- R F Bruinsma
- Department of Physics and Astronomy, The University of California at Los Angeles, Los Angeles, CA 90049, USA.
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19
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Stockley PG, Ashcroft AE, Francese S, Thompson GS, Ranson NA, Smith AM, Homans SW, Stonehouse NJ. Dissecting the Fine Details of Assembly of aT = 3 Phage Capsid. ACTA ACUST UNITED AC 2005. [DOI: 10.1080/10273660500149869] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
The RNA bacteriophages represent ideal model systems in which to probe the detailed assembly pathway for the formation of aT = 3 quasi-equivalent capsid. For MS2, the assembly reaction can be probedin vitrousing acid disassembled coat protein subunits and a short (19 nt) RNA stem-loop that acts as the translational operator of the replicase gene and leads to sequence-specific sequestration and packaging of the cognate phage RNAin vivo. Reassembly reactions can be initiated by mixing these components at neutral pH. The molecular basis of the sequence-specific RNA–protein interaction is now well understood. Recent NMR studies on the protein demonstrate extensive mobility in the loops of the polypeptide that alter their conformations to form the quasi-equivalent conformers of the final capsid. It seems reasonable to assume that RNA binding results in reduction of this flexibility. However, mass spectrometry suggests that these RNA–protein complexes may only provide one type of quasi-equivalent capsid building block competent to form five-fold axes but not the full shell. Work with longer RNAs suggests that the RNA may actively template the assembly pathway providing a partial explanation of how conformers are selected in the growing shell.
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Affiliation(s)
- P. G. Stockley
- Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds LS2 9JT, UK
| | - A. E. Ashcroft
- Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds LS2 9JT, UK
| | - S. Francese
- Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds LS2 9JT, UK
| | - G. S. Thompson
- Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds LS2 9JT, UK
| | - N. A. Ranson
- Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds LS2 9JT, UK
| | - A. M. Smith
- Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds LS2 9JT, UK
| | - S. W. Homans
- Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds LS2 9JT, UK
| | - N. J. Stonehouse
- Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds LS2 9JT, UK
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20
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Horn WT, Convery MA, Stonehouse NJ, Adams CJ, Liljas L, Phillips SEV, Stockley PG. The crystal structure of a high affinity RNA stem-loop complexed with the bacteriophage MS2 capsid: further challenges in the modeling of ligand-RNA interactions. RNA (NEW YORK, N.Y.) 2004; 10:1776-1782. [PMID: 15496523 PMCID: PMC1370665 DOI: 10.1261/rna.7710304] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/27/2004] [Accepted: 08/16/2004] [Indexed: 05/24/2023]
Abstract
We have determined the structure to 2.8 A of an RNA aptamer (F5), containing 2'-deoxy-2-aminopurine (2AP) at the -10 position, complexed with MS2 coat protein by soaking the RNA into precrystallised MS2 capsids. The -10 position of the RNA is an important determinant of binding affinity for coat protein. Adenine at this position in other RNA stem-loops makes three hydrogen bonds to protein functional groups. Substituting 2AP for the -10 adenine in the F5 aptamer yields an RNA with the highest yet reported affinity for coat protein. The refined X-ray structure shows that the 2AP base makes an additional hydrogen bond to the protein compared to adenine that is presumably the principal origin of the increased affinity. There are also slight changes in phosphate backbone positions compared to unmodified F5 that probably also contribute to affinity. Such phosphate movements are common in structures of RNAs bound to the MS2 T = 3 protein shell and highlight problems for de novo design of RNA binding ligands.
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Affiliation(s)
- Wilf T Horn
- Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds LS2 9JT, United Kingdom
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21
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Helgstrand C, Grahn E, Moss T, Stonehouse NJ, Tars K, Stockley PG, Liljas L. Investigating the structural basis of purine specificity in the structures of MS2 coat protein RNA translational operator hairpins. Nucleic Acids Res 2002; 30:2678-85. [PMID: 12060685 PMCID: PMC117284 DOI: 10.1093/nar/gkf371] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
We have determined the structures of complexes between the phage MS2 coat protein and variants of the replicase translational operator in order to explore the sequence specificity of the RNA-protein interaction. The 19-nt RNA hairpins studied have substitutions at two positions that have been shown to be important for specific binding. At one of these positions, -10, which is a bulged adenosine (A) in the stem of the wild-type operator hairpin, substitutions were made with guanosine (G), cytidine (C) and two non-native bases, 2-aminopurine (2AP) and inosine (I). At the other position, -7 in the hairpin loop, the native adenine was substituted with a cytidine. Of these, only the G-10, C-10 and C-7 variants showed interpretable density for the RNA hairpin. In spite of large differences in binding affinities, the structures of the variant complexes are very similar to the wild-type operator complex. For G-10 substitutions in hairpin variants that can form bulges at alternative places in the stem, the binding affinity is low and a partly disordered conformation is seen in the electron density maps. The affinity is similar to that of wild-type when the base pairs adjacent to the bulged nucleotide are selected to avoid alternative conformations. Both purines bind in a very similar way in a pocket in the protein. In the C-10 variant, which has very low affinity, the cytidine is partly inserted in the protein pocket rather than intercalated in the RNA stem. Substitution of the wild-type adenosine at position -7 by pyrimidines gives strongly reduced affinities, but the structure of the C-7 complex shows that the base occupies the same position as the A-7 in the wild-type RNA. It is stacked in the RNA and makes no direct contact with the protein.
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Affiliation(s)
- Charlotte Helgstrand
- Department of Cell and Molecular Biology, Uppsala University, Box 596, SE-751 24 Uppsala, Sweden
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22
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Lago H, Parrott AM, Moss T, Stonehouse NJ, Stockley PG. Probing the kinetics of formation of the bacteriophage MS2 translational operator complex: identification of a protein conformer unable to bind RNA. J Mol Biol 2001; 305:1131-44. [PMID: 11162119 DOI: 10.1006/jmbi.2000.4355] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We have investigated the kinetics of complex formation between bacteriophage MS2 coat protein subunits and synthetic RNA fragments encompassing the natural translational operator site, or the consensus sequences of three distinct RNA aptamer families, which are known to bind to the same site on the protein. Reactions were assayed using stopped-flow fluorescence spectroscopy and either the intrinsic tryptophan fluorescence of the protein or the signals from RNA fragments site-specifically substituted with the fluorescent adenosine analogue 2'-deoxy, 2-aminopurine. The kinetics observed were independent of the fluorophore being monitored or its position within the complex, indicating that the data report global events occurring during complex formation. Competition assays show that the complex being formed consists of a single coat protein dimer and one RNA molecule. The binding reaction is at least biphasic. The faster phase, constituting 80-85 % of the amplitude, is a largely diffusion driven RNA-protein interaction (k1 approximately 2x10(9) M(-1) s(-1)). The salt dependence of the forward reaction and the similarities of the on-rates of lower-affinity RNA fragments are consistent with a diffusion-controlled step dominated by electrostatic steering. The slower phase is independent of reactant concentration, and appears to correspond to isomerisation of the coat protein subunit(s) prior to RNA binding (k(iso) approximately 0.23 s(-1)). Measurements with a coat protein mutant (Pro78Asn) show that this phase is not due to cis-trans isomerisation at this residue. The conformational changes in the protein ligand during formation of an RNA-protein complex might play a role in the triggering of capsid self-assembly and a model for this is discussed.
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Affiliation(s)
- H Lago
- Astbury Centre for Structural Molecular Biology, Faculty of Biological Sciences, University of Leeds, Leeds, LS2 9JT, UK
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23
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Axblom C, Tars K, Fridborg K, Orna L, Bundule M, Liljas L. Structure of phage fr capsids with a deletion in the FG loop: implications for viral assembly. Virology 1998; 249:80-8. [PMID: 9740779 DOI: 10.1006/viro.1998.9279] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The loop between beta-strands F and G in the coat protein of small RNA bacteriophages forms the interactions at the fivefold and threefold (quasi-sixfold) icosahedral axes. In many cases, mutations in this region renders the coat protein unable to form capsids. This FG loop has therefore been suggested to be of major importance for the virus assembly process by guiding the assembly and helping to define the correct curvature of the virus shell. We have determined the crystal structure of a phage fr capsid where the coat protein has a four-residue deletion in the FG loop. This mutant retains the ability to form virus capsids of normal size but has a significantly lower temperature stability than the wild type. The structure reveals that the mutated loops are flexible and too short to interact with each other. This seems incompatible with a role of the FG loop in the regulation of capsid size.
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Affiliation(s)
- C Axblom
- Department of Molecular Biology, Uppsala University, Uppsala, S-751 24, Sweden
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24
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Wang S, True HL, Seitz EM, Bennett KA, Fouts DE, Gardner JF, Celander DW. Direct genetic selection of two classes of R17/MS2 coat proteins with altered capsid assembly properties and expanded RNA-binding activities. Nucleic Acids Res 1997; 25:1649-57. [PMID: 9092675 PMCID: PMC146620 DOI: 10.1093/nar/25.8.1649] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
RNA challenge phages are derivatives of bacteriophage P22 that enable direct genetic selection for a specific RNA-protein interaction. The bacteriophage P22 R17 encodes a wild-type R17 operator site and undergoes lysogenic development following infection of susceptible bacterial strains that express the R17/MS2 coat protein. A P22 R17 derivative with an OcRNA site (P22 R17 [A(-10)U]) develops lytically following infection of these strains. RNA challenge phages can be used to isolate second-site coat protein suppressors that recognize an OcRNA sequence by selecting for lysogens with a P22 R17 [Oc] phage derivative. The bacteriophage derivative P22 R17 [A(-10)U] was used in one such scheme to isolate two classes of genes that encode R17 coat proteins with altered capsid assembly properties and expanded RNA-binding characteristics. These mutations map outside the RNA-binding surface and include amino acid substitutions that interfere with interactions between coat protein dimers in the formation of the stable phage capsid. One class of mutants encodes substitutions at the highly conserved first and second positions of the mature coat protein. N-terminal sequence analysis of these mutants reveals that coat proteins with substitutions only at position 1 are defective in post-translational processing of the initiator methionine. All selected proteins possess expanded RNA-binding properties since they direct efficient lysogen formation for P22 R17 and P22 R17 [A(-10)U]; however, bacterial strains that express the protein mutants remain sensitive to lytic infection by other P22 R17 [Oc] bacteriophages. The described selection strategy provides a novel genetic approach to dissecting protein structure within RNA-binding proteins.
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Affiliation(s)
- S Wang
- Department of Microbiology and College of Medicine, University of Illinois at Urbana-Champaign, B103 Chemical and Life Sciences Laboratory, 601 South Goodwin Avenue, Urbana, IL 61801, USA
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25
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Qu F, Morris TJ. Encapsidation of turnip crinkle virus is defined by a specific packaging signal and RNA size. J Virol 1997; 71:1428-35. [PMID: 8995668 PMCID: PMC191199 DOI: 10.1128/jvi.71.2.1428-1435.1997] [Citation(s) in RCA: 101] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
A protoplast infection assay has been used to reliably examine the viral RNA encapsidation of turnip crinkle virus (TCV). Analysis of the encapsidation of various mutant viral RNAs revealed that a 186-nucleotide (nt) region at the 3' end of the coat protein (CP) gene, with a bulged hairpin loop of 28 nt as its most essential element, was indispensable for TCV RNA encapsidation. When RNA fragments containing the 186-nt region were used to replace the CP gene of a different virus, tomato bushy stunt virus, the resulting chimeric viral RNAs were encapsidated into TCV virions. Furthermore, analysis of the encapsidated chimeric RNA species established that the RNA size was an important determinant of the TCV assembly process.
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Affiliation(s)
- F Qu
- School of Biological Sciences, University of Nebraska-Lincoln, 68588-0118, USA
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26
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Willis MC, LeCuyer KA, Meisenheimer KM, Uhlenbeck OC, Koch TH. An RNA-protein contact determined by 5-bromouridine substitution, photocrosslinking and sequencing. Nucleic Acids Res 1994; 22:4947-52. [PMID: 7800485 PMCID: PMC523761 DOI: 10.1093/nar/22.23.4947] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
An analogue of the replicase translational operator of bacteriophage R17, that contains a 5-bromouridine at position -5 (RNA 1), complexes with a dimer of the coat protein and photocrosslinks to the coat protein in high yield upon excitation at 308 nm with a xenon chloride excimer laser. Tryptic digestion of the crosslinked nucleoprotein complex followed by Edman degradation of the tryptic fragment bearing the RNA indicates crosslinking to tyrosine 85 of the coat protein. A control experiment with a Tyr 85 to Ser 85 variant coat protein showed binding but no photocrosslinking at saturating protein concentration. This is consistent with the observation from model compound studies of preferential photocrosslinking of BrU to the electron rich aromatic amino acids tryptophan, tyrosine, and histidine with 308 nm excitation.
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Affiliation(s)
- M C Willis
- Department of Chemistry, University of Colorado, Boulder 80309-0215
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27
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Johnson JE. Viruses getting their heads together. Curr Biol 1991; 1:287-9. [PMID: 15336099 DOI: 10.1016/0960-9822(91)90086-c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Affiliation(s)
- J E Johnson
- Department of Biological Sciences, Purdue University, Lilly Hall, West Lafayette, Indiana 47907, USA
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28
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Gott JM, Willis MC, Koch TH, Uhlenbeck OC. A specific, UV-induced RNA-protein cross-link using 5-bromouridine-substituted RNA. Biochemistry 1991; 30:6290-5. [PMID: 1711897 DOI: 10.1021/bi00239a030] [Citation(s) in RCA: 49] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The well-characterized RNA binding site of the bacteriophage R17 coat protein has been used to investigate the cross-linking of protein to 5-bromouridine (BrU)-substituted RNA using medium-wavelength UV light. We have demonstrated a specific RNA-protein cross-link and identified the site on the RNA of protein attachment. Formation of the covalent complex is dependent upon the presence of BrU at position -5 of the RNA and specific binding of the RNA by coat protein. The amount of cross-linking increases with time and depends on the light source and conditions used. Irradiations using a broad-spectrum UV transilluminator (peak at 312 nm) or monochromatic XeCl excimer laser (308 nm) gave levels of cross-linking exceeding 20 and 50%, respectively. The quantum yield of photo-cross-linking, determined with 308-nm excitation, was 0.003. While little strand breakage or debromination of the RNA occurred, significant protein photodamage was observed.
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Affiliation(s)
- J M Gott
- Department of Chemistry and Biochemistry, University of Colorado, Boulder 80309-0215
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Witherell GW, Gott JM, Uhlenbeck OC. Specific interaction between RNA phage coat proteins and RNA. PROGRESS IN NUCLEIC ACID RESEARCH AND MOLECULAR BIOLOGY 1991; 40:185-220. [PMID: 2031083 DOI: 10.1016/s0079-6603(08)60842-9] [Citation(s) in RCA: 149] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Affiliation(s)
- G W Witherell
- Department of Chemistry and Biochemistry, University of Colorado, Boulder 80309
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Valegård K, Liljas L, Fridborg K, Unge T. The three-dimensional structure of the bacterial virus MS2. Nature 1990; 345:36-41. [PMID: 2330049 DOI: 10.1038/345036a0] [Citation(s) in RCA: 293] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
The structure of the icosahedral bacteriophage MS2 has been determined to 3.3 A resolution by X-ray crystallography. The phase determination involved both molecular replacement at low resolution using a known structure and heavy-atom substitution. The coat protein has no structural similarity to that of any other known RNA virus.
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Affiliation(s)
- K Valegård
- Department of Molecular Biology, Uppsala University, Sweden
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31
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Russel M, Model P. Genetic analysis of the filamentous bacteriophage packaging signal and of the proteins that interact with it. J Virol 1989; 63:3284-95. [PMID: 2746731 PMCID: PMC250900 DOI: 10.1128/jvi.63.8.3284-3295.1989] [Citation(s) in RCA: 65] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
The single-stranded DNA of filamentous phages (f1, fd, M13, Ike) contains a region that can fold into a hairpin structure that serves to earmark the DNA for encapsidation. Second-site suppressor mutants of f1 that can compensate for deletion of this packaging signal have been isolated and characterized. The mutations lie in three genes, two that encode virion proteins located at the end of the particle that is first to emerge from the cell, the end at which the packaging signal is located, and the third in a gene whose product is required for assembly but which is not itself a part of the virion. Analysis of base substitution and deletion mutations in the packaging signal suggests that both structural and sequence elements are important to its proper function.
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Affiliation(s)
- M Russel
- Rockefeller University, New York, New York 10021-6399
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Beckett D, Wu HN, Uhlenbeck OC. Roles of operator and non-operator RNA sequences in bacteriophage R17 capsid assembly. J Mol Biol 1988; 204:939-47. [PMID: 3221401 DOI: 10.1016/0022-2836(88)90053-8] [Citation(s) in RCA: 73] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
In order to understand the role of sequences other than the translational operator on bacteriophage R17 assembly, in vitro capsid assembly was studied with R17 coat protein and a variety of RNAs. For a series of RNA oligomers of the same chain length, sequences that bind coat protein dimer with a lower affinity require higher concentrations of RNA and protein for assembly. Among a series of non-specific RNA molecules of differing lengths, lower protein and RNA concentrations are required for assembly of capsids containing longer RNAs. For RNA molecules of any length, the presence of a single high-affinity translational operator sequence lowered the concentration requirements for capsid assembly. However, the advantage for encapsidation provided by the operator sequence is small for large RNA molecules. The experiments indicate that in the overall assembly process the interaction of coat protein with non-specific sequences is at least as important as its interaction with the specific translational operator sequence. In light of the data, a mechanism of achieving selective packaging of the R17 genomic RNA in vivo is discussed.
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Affiliation(s)
- D Beckett
- University of Colorado, Department of Chemistry and Biochemistry, Boulder 80309-0215
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Tomoeda M, Inuzuka M, Date T. Bacterial sex pili. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 1976; 30:23-56. [PMID: 1101296 DOI: 10.1016/0079-6107(76)90004-3] [Citation(s) in RCA: 40] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
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Dodds JA, Hamilton RI. Structural interactions between viruses as a consequence of mixed infections. Adv Virus Res 1976; 20:33-86. [PMID: 818891 DOI: 10.1016/s0065-3527(08)60501-1] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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Goodman RM, Ross AF. Independent assembly of virions in tobacco doubly infected by potato virus X and potato virus Y or tobacco mosaic virus. Virology 1974; 59:314-8. [PMID: 4826211 DOI: 10.1016/0042-6822(74)90228-1] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
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Peterson JF, Brakke MK. Genomic masking in mixed infections with brome mosaic and barley stripe mosaic viruses. Virology 1973; 51:174-82. [PMID: 4734115 DOI: 10.1016/0042-6822(73)90377-2] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
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Miyake T, Shiba T. Formation of hybrid particles in RNA phages. I. Hybrid particles between RNA phages SP (IVa) and FI(IVb). Virology 1971; 43:675-84. [PMID: 4940970 DOI: 10.1016/0042-6822(71)90291-1] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
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