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Identification of cis-acting elements on positive-strand subgenomic mRNA required for the synthesis of negative-strand counterpart in bovine coronavirus. Viruses 2014; 6:2938-59. [PMID: 25080125 PMCID: PMC4147681 DOI: 10.3390/v6082938] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2014] [Revised: 07/12/2014] [Accepted: 07/15/2014] [Indexed: 01/06/2023] Open
Abstract
It has been demonstrated that, in addition to genomic RNA, sgmRNA is able to serve as a template for the synthesis of the negative-strand [(−)-strand] complement. However, the cis-acting elements on the positive-strand [(+)-strand] sgmRNA required for (−)-strand sgmRNA synthesis have not yet been systematically identified. In this study, we employed real-time quantitative reverse transcription polymerase chain reaction to analyze the cis-acting elements on bovine coronavirus (BCoV) sgmRNA 7 required for the synthesis of its (−)-strand counterpart by deletion mutagenesis. The major findings are as follows. (1) Deletion of the 5'-terminal leader sequence on sgmRNA 7 decreased the synthesis of the (−)-strand sgmRNA complement. (2) Deletions of the 3' untranslated region (UTR) bulged stem-loop showed no effect on (−)-strand sgmRNA synthesis; however, deletion of the 3' UTR pseudoknot decreased the yield of (−)-strand sgmRNA. (3) Nucleotides positioned from −15 to −34 of the sgmRNA 7 3'-terminal region are required for efficient (−)-strand sgmRNA synthesis. (4) Nucleotide species at the 3'-most position (−1) of sgmRNA 7 is correlated to the efficiency of (−)-strand sgmRNA synthesis. These results together suggest, in principle, that the 5'- and 3'-terminal sequences on sgmRNA 7 harbor cis-acting elements are critical for efficient (−)-strand sgmRNA synthesis in BCoV.
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The 3'-terminal 55 nucleotides of bovine coronavirus defective interfering RNA harbor cis-acting elements required for both negative- and positive-strand RNA synthesis. PLoS One 2014; 9:e98422. [PMID: 24852421 PMCID: PMC4031142 DOI: 10.1371/journal.pone.0098422] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2014] [Accepted: 05/02/2014] [Indexed: 01/21/2023] Open
Abstract
The synthesis of the negative-strand [(−)-strand] complement of the ∼30 kilobase, positive-strand [(+)-strand] coronaviral genome is a necessary early step for genome replication. The identification of cis-acting elements required for (−)-strand RNA synthesis in coronaviruses, however, has been hampered due to insufficiencies in the techniques used to detect the (−)-strand RNA species. Here, we employed a method of head-to-tail ligation and real-time quantitative reverse transcription polymerase chain reaction (qRT-PCR) to detect and quantitate the synthesis of bovine coronavirus (BCoV) defective interfering (DI) RNA (−) strands. Furthermore, using the aforementioned techniques along with Northern blot assay, we specifically defined the cis-acting RNA elements within the 3′-terminal 55 nucleotides (nts) which function in the synthesis of (−)- or (+)-strand BCoV DI RNA. The major findings are as follows: (i) nts from -5 to -39 within the 3′-terminal 55 nts are the cis-acting elements responsible for (−)-strand BCoV DI RNA synthesis, (ii) nts from −3 to −34 within the 3′-terminal 55 nts are cis-acting elements required for (+)-strand BCoV DI RNA synthesis, and (iii) the nucleotide species at the 3′-most position (−1) is important, but not critical, for both (−)- and (+)-strand BCoV DI RNA synthesis. These results demonstrate that the 3′-terminal 55 nts in BCoV DI RNA harbor cis-acting RNA elements required for both (−)- and (+)-strand DI RNA synthesis and extend our knowledge on the mechanisms of coronavirus replication. The method of head-to-tail ligation and qRT-PCR employed in the study may also be applied to identify other cis-acting elements required for (−)-strand RNA synthesis in coronaviruses.
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Romero-López C, Berzal-Herranz A. Unmasking the information encoded as structural motifs of viral RNA genomes: a potential antiviral target. Rev Med Virol 2013; 23:340-54. [PMID: 23983005 PMCID: PMC7169113 DOI: 10.1002/rmv.1756] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2013] [Revised: 07/23/2013] [Accepted: 07/24/2013] [Indexed: 02/05/2023]
Abstract
RNA viruses show enormous capacity to evolve and adapt to new cellular and molecular contexts, a consequence of mutations arising from errors made by viral RNA-dependent RNA polymerase during replication. Sequence variation must occur, however, without compromising functions essential for the completion of the viral cycle. RNA viruses are safeguarded in this respect by their genome carrying conserved information that does not code only for proteins but also for the formation of structurally conserved RNA domains that directly perform these critical functions. Functional RNA domains can interact with other regions of the viral genome and/or proteins to direct viral translation, replication and encapsidation. They are therefore potential targets for novel therapeutic strategies. This review summarises our knowledge of the functional RNA domains of human RNA viruses and examines the achievements made in the design of antiviral compounds that interfere with their folding and therefore their function.
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Affiliation(s)
- Cristina Romero-López
- Instituto de Parasitología y Biomedicina 'López-Neyra', IPBLN-CSIC, PTS Granada, Armilla, Granada, Spain
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Liu P, Yang D, Carter K, Masud F, Leibowitz JL. Functional analysis of the stem loop S3 and S4 structures in the coronavirus 3'UTR. Virology 2013; 443:40-7. [PMID: 23683838 PMCID: PMC3700632 DOI: 10.1016/j.virol.2013.04.021] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2013] [Revised: 03/20/2013] [Accepted: 04/22/2013] [Indexed: 12/22/2022]
Abstract
We designed a series of mutations to separately destabilize two helical stems (designated S3 and S4) predicted by a covariation-based model of the coronavirus 3′UTR (Zust et al., 2008). Mouse hepatitis virus genomes containing three or four nucleotide mutations that destabilize either S3 or S4 were viable, whereas genomes carrying these mutations in both S3 and S4 were not viable. A genome carrying these mutations in S3 and S4 plus compensatory mutations restoring base-pairing yielded a virus with wild type phenotype. Larger mutations which completely disrupt S3 or S4 generated various phenotypes. Mutations opening up S3 were lethal. Disruptions of S4 generated both viable and lethal mutants. Genomes carrying the original mutations in S3 or S4 plus compensatory mutations restoring base pairing were viable and had robust growth phenotypes. These results support the Zust model for the coronavirus 3′UTR and suggest that the S3 stem is required for virus viability. Genetic studies of MHV 3′UTR RNA secondary structure support the Zust et al. model. The 3′UTR S3 helical stem is required for virus viability. The 3′UTR S4 helical stem is not required for virus viability.
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Affiliation(s)
- Pinghua Liu
- Department of Microbial and Molecular Pathogenesis, Texas A&M HSC College of Medicine, 407 Reynolds Medical Building, College Station, TX 77843-1114, USA.
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Liu X, Shao Y, Ma H, Sun C, Zhang X, Li C, Han Z, Yan B, Kong X, Liu S. Comparative analysis of four Massachusetts type infectious bronchitis coronavirus genomes reveals a novel Massachusetts type strain and evidence of natural recombination in the genome. INFECTION GENETICS AND EVOLUTION 2012. [PMID: 23178317 PMCID: PMC7106298 DOI: 10.1016/j.meegid.2012.09.016] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 10/31/2022]
Abstract
Four Massachusetts-type (Mass-type) strains of infectious bronchitis coronavirus (IBV) were compared genetically with the pathogenic M41 and H120 vaccine strains using the complete genomic sequences. The results revealed that strains ck/CH/LNM/091017 and ck/CH/LDL/101212 were closely related to the H120 vaccine, which suggests that they might represent re-isolations of vaccine strains or variants of vaccine strains that have resulted from the accumulated point mutations after several passages in chickens. In contrast, strains ck/CH/LHLJ/07VII and ck/CH/LHLJ/100902 had a close genetic relationship with the pathogenic M41 strain. In addition, molecular markers have been identified that distinguish between field and vaccine (or vaccine-like) Mass-type viruses, which may be able to differentiate between field and vaccine strains for diagnostic purposes. Phylogenetic analysis, and pairwise comparison of full-length genomes and the nine genes, identified the occurrence of recombination events in the genome of strain CK/VH/LHLJ/07VII, which suggests that this virus originated from recombination events between M41- and H120-like strains at the switch site located at the 3' end of the nucleocapsid (N) genes. To our knowledge, this is the first time that evidence for the evolution and natural recombination under field conditions between Mass-type pathogenic and vaccinal IBV strains has been documented. These findings provide insights into the emergence and evolution of the Mass-type IB coronaviruses and may help to explain the emergence of Mass-type IBV in chicken flocks all over the world.
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Affiliation(s)
- Xiaoli Liu
- Division of Avian Infectious Diseases, National Key Laboratory of Veterinary Biotechnology, Harbin Veterinary Research Institute, The Chinese Academy of Agricultural Sciences, Harbin 150001, People's Republic of China
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56
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Guan BJ, Su YP, Wu HY, Brian DA. Genetic evidence of a long-range RNA-RNA interaction between the genomic 5' untranslated region and the nonstructural protein 1 coding region in murine and bovine coronaviruses. J Virol 2012; 86:4631-43. [PMID: 22345457 PMCID: PMC3318640 DOI: 10.1128/jvi.06265-11] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2011] [Accepted: 02/02/2012] [Indexed: 01/25/2023] Open
Abstract
Higher-order RNA structures in the 5' untranslated regions (UTRs) of the mouse hepatitis coronavirus (MHV) and bovine coronavirus (BCoV), separate species in the betacoronavirus genus, appear to be largely conserved despite an ∼36% nucleotide sequence divergence. In a previous study, each of three 5'-end-proximal cis-acting stem-loop domains in the BCoV genome, I/II, III, and IV, yielded near-wild-type (wt) MHV phenotypes when used by reverse genetics to replace its counterpart in the MHV genome. Replacement with the BCoV 32-nucleotide (nt) inter-stem-loop fourth domain between stem-loops III and IV, however, required blind cell passaging for virus recovery. Here, we describe suppressor mutations within the transplanted BCoV 32-nt domain that along with appearance of potential base pairings identify an RNA-RNA interaction between this domain and a 32-nt region ∼200 nt downstream within the nonstructural protein 1 (Nsp1)-coding region. Mfold and phylogenetic covariation patterns among similarly grouped betacoronaviruses support this interaction, as does cotransplantation of the BCoV 5' UTR and its downstream base-pairing domain. Interestingly, cotransplantation of the BCoV 5' UTR and BCoV Nsp1 coding region directly yielded an MHV wt-like phenotype, which demonstrates a cognate interaction between these two BCoV regions, which in the MHV genome act in a fully interspecies-compliant manner. Surprisingly, the 30-nt inter-stem-loop domain in the MHV genome can be deleted and viral progeny, although debilitated, are still produced. These results together identify a previously undescribed long-range RNA-RNA interaction between the 5' UTR and Nsp1 coding region in MHV-like and BCoV-like betacoronaviruses that is cis acting for viral fitness but is not absolutely required for viral replication in cell culture.
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Affiliation(s)
| | - Yu-Pin Su
- Biomedical and Diagnostic Sciences, University of Tennessee College of Veterinary Medicine, Knoxville, Tennessee, USA
| | - Hung-Yi Wu
- Biomedical and Diagnostic Sciences, University of Tennessee College of Veterinary Medicine, Knoxville, Tennessee, USA
| | - David A. Brian
- Departments of Microbiology
- Biomedical and Diagnostic Sciences, University of Tennessee College of Veterinary Medicine, Knoxville, Tennessee, USA
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Stammler SN, Cao S, Chen SJ, Giedroc DP. A conserved RNA pseudoknot in a putative molecular switch domain of the 3'-untranslated region of coronaviruses is only marginally stable. RNA (NEW YORK, N.Y.) 2011; 17:1747-59. [PMID: 21799029 PMCID: PMC3162339 DOI: 10.1261/rna.2816711] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/12/2011] [Accepted: 06/20/2011] [Indexed: 05/26/2023]
Abstract
The 3'-untranslated region (UTR) of the group 2 coronavirus mouse hepatitis virus (MHV) genome contains a predicted bulged stem-loop (designated P0ab), a conserved cis-acting pseudoknot (PK), and a more distal stem-loop (designated P2). Base-pairing to create the pseudoknot-forming stem (P1(pk)) is mutually exclusive with formation of stem P0a at the base of the bulged stem-loop; as a result, the two structures cannot be present simultaneously. Herein, we use thermodynamic methods to evaluate the ability of individual subdomains of the 3' UTR to adopt a pseudoknotted conformation. We find that an RNA capable of forming only the predicted PK (58 nt; 3' nucleotides 241-185) adopts the P2 stem-loop with little evidence for P1(pk) pairing in 0.1 M KCl and the absence of Mg(2+); as Mg(2+) or 1 M KCl is added, a new thermal unfolding transition is induced and assignable to P1(pk) pairing. The P1(pk) helix is only marginally stable, ΔG(25) ≈ 1.2 ± 0.3 kcal/mol (5.0 mM Mg(2+), 100 mM K(+)), and unfolded at 37°C. Similar findings characterize an RNA 5' extended through the P0b helix only (89 nt; 294-185). In contrast, an RNA capable of forming either the P0a helix or the pseudoknot (97 nt; 301-185) forms no P1(pk) helix. Thermal unfolding simulations are fully consistent with these experimental findings. These data reveal that the PK forms weakly and only when the competing double-hairpin structure cannot form; in the UTR RNA, the double hairpin is the predominant conformer under all solution conditions.
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Affiliation(s)
- Suzanne N. Stammler
- Department of Chemistry, Texas A&M University, College Station, Texas 77843-2128, USA
- Department of Biochemistry and Biophysics, Texas A&M University, College Station, Texas 77843-2128, USA
| | - Song Cao
- Department of Physics, University of Missouri, Columbia, Missouri 65211, USA
- Department of Biochemistry, University of Missouri, Columbia, Missouri 65211, USA
| | - Shi-Jie Chen
- Department of Physics, University of Missouri, Columbia, Missouri 65211, USA
- Department of Biochemistry, University of Missouri, Columbia, Missouri 65211, USA
| | - David P. Giedroc
- Department of Biochemistry and Biophysics, Texas A&M University, College Station, Texas 77843-2128, USA
- Department of Chemistry, Indiana University, Bloomington, Indiana 47405-7102, USA
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An optimal cis-replication stem-loop IV in the 5' untranslated region of the mouse coronavirus genome extends 16 nucleotides into open reading frame 1. J Virol 2011; 85:5593-605. [PMID: 21430057 DOI: 10.1128/jvi.00263-11] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
The 288-nucleotide (nt) 3' untranslated region (UTR) in the genome of the bovine coronavirus (BCoV) and 339-nt 3' UTR in the severe acute respiratory syndrome (SARS) coronavirus (SCoV) can each replace the 301-nt 3' UTR in the mouse hepatitis coronavirus (MHV) for virus replication, thus demonstrating common 3' cis-replication signals. Here, we show that replacing the 209-nt MHV 5' UTR with the ∼63%-sequence-identical 210-nt BCoV 5' UTR by reverse genetics does not yield viable virus, suggesting 5' end signals are more stringent or possibly are not strictly 5' UTR confined. To identify potential smaller, 5'-common signals, each of three stem-loop (SL) signaling domains and one inter-stem-loop domain from the BCoV 5' UTR was tested by replacing its counterpart in the MHV genome. The SLI/II domain (nucleotides 1 to 84) and SLIII domain (nucleotides 85 to 141) each immediately enabled near-wild-type (wt) MHV-like progeny, thus behaving similarly to comparable 5'-proximal regions of the SCoV 5' UTR as shown by others. The inter-stem-loop domain (nt 142 to 173 between SLs III and IV) enabled small plaques only after genetic adaptation. The SLIV domain (nt 174 to 210) required a 16-nt extension into BCoV open reading frame 1 (ORF1) for apparent stabilization of a longer BCoV SLIV (nt 174 to 226) and optimal virus replication. Surprisingly, pleiomorphic SLIV structures, including a terminal loop deletion, were found among debilitated progeny from intra-SLIV chimeras. The results show the inter-stem-loop domain to be a potential novel species-specific cis-replication element and that cis-acting SLIV in the viral genome extends into ORF1 in a manner that stabilizes its lower stem and is thus not 5' UTR confined.
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59
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The solution structure of coronaviral stem-loop 2 (SL2) reveals a canonical CUYG tetraloop fold. FEBS Lett 2011; 585:1049-53. [PMID: 21382373 PMCID: PMC3086565 DOI: 10.1016/j.febslet.2011.03.002] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2010] [Revised: 02/08/2011] [Accepted: 03/01/2011] [Indexed: 11/21/2022]
Abstract
The transcription and replication of the severe acute respiratory syndrome (SARS) coronavirus (SARS‐CoV) is regulated by specific viral genome sequences within 5′‐ and 3′‐untranslated regions (5′‐UTR and 3′‐UTR). Here we report the solution structure of 5′‐UTR derived stem‐loop 2 (SL2) of SARS‐CoV determined by NMR spectroscopy. The highly conserved pentaloop of SL2 is stacked on 5‐bp stem and adopts a canonical CUYG tetraloop fold with the 3′ nucleotide (U51) flipped out of the stack. The significance of this structure in the context of a previous mutagenesis analysis of SL2 function in replication of the related group 2 coronavirus, mouse hepatitis virus, is discussed.
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60
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Sola I, Mateos-Gomez PA, Almazan F, Zuñiga S, Enjuanes L. RNA-RNA and RNA-protein interactions in coronavirus replication and transcription. RNA Biol 2011; 8:237-48. [PMID: 21378501 PMCID: PMC3230552 DOI: 10.4161/rna.8.2.14991] [Citation(s) in RCA: 101] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2010] [Revised: 01/17/2011] [Accepted: 01/19/2011] [Indexed: 02/07/2023] Open
Abstract
Coronavirus (CoV) RNA synthesis includes the replication of the viral genome, and the transcription of sgRNAs by a discontinuous mechanism. Both processes are regulated by RNA sequences such as the 5' and 3' untranslated regions (UTRs), and the transcription regulating sequences (TRSs) of the leader (TRS-L) and those preceding each gene (TRS-Bs). These distant RNA regulatory sequences interact with each other directly and probably through protein-RNA and protein-protein interactions involving viral and cellular proteins. By analogy to other plus-stranded RNA viruses, such as polioviruses, in which translation and replication switch involves a cellular factor (PCBP) and a viral protein (3CD) it is conceivable that in CoVs the switch between replication and transcription is also associated with the binding of proteins that are specifically recruited by the replication or transcription complexes. Complexes between RNA motifs such as TRS-L and the TRS-Bs located along the CoV genome are probably formed previously to the transcription start, and most likely promote template-switch of the nascent minus RNA to the TRS-L region. Many cellular proteins interacting with regulatory CoV RNA sequences are members of the heterogeneous nuclear ribonucleoprotein (hnRNP) family of RNA-binding proteins, involved in mRNA processing and transport, which shuttle between the nucleus and the cytoplasm. In the context of CoV RNA synthesis, these cellular ribonucleoproteins might also participate in RNA-protein complexes to bring into physical proximity TRS-L and distant TRS-B, as proposed for CoV discontinuous transcription. In this review, we summarize RNA-RNA and RNA-protein interactions that represent modest examples of complex quaternary RNA-protein structures required for the fine-tuning of virus replication. Design of chemically defined replication and transcription systems will help to clarify the nature and activity of these structures.
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Affiliation(s)
- Isabel Sola
- Department of Molecular and Cell Biology, CNB, CSIC, Cantoblanco, Madrid, Spain
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61
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Sun Z, Liu C, Tan F, Gao F, Liu P, Qin A, Yuan S. Identification of dispensable nucleotide sequence in 3' untranslated region of porcine reproductive and respiratory syndrome virus. Virus Res 2010; 154:38-47. [PMID: 20833212 PMCID: PMC7114379 DOI: 10.1016/j.virusres.2010.08.027] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2010] [Revised: 08/18/2010] [Accepted: 08/27/2010] [Indexed: 01/03/2023]
Abstract
The 3′ untranslated region (UTR) of porcine arterivirus genome plays a pivotal role for virus replication, yet the properties of 3′ UTR remain largely undefined. We conducted site-directed mutagenesis to the 3′ UTR of the type II porcine reproductive and respiratory syndrome virus (PRRSV). Serial deletions of the 3′ UTR showed that at least 40 nucleotides immediately following the ORF7 stop codon were dispensable for the viability of PRRSV in cultured cells. We then constructed a chimeric PRRSV cDNA clone using type II PRRSV as the backbone containing the 3′ UTR from the type I PRRSV. The chimeric virus was viable and shared similar properties with the parental virus. Our results provided the first description of the 40nt dispensable region in type I PRRSV 3′ UTR, and further predicted structure demonstrated that the high-order structure of 3′ UTR might play significant roles in its function.
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Affiliation(s)
- Zhi Sun
- Department of Swine Infectious Diseases, Shanghai Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Shanghai 200241, China
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62
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Abstract
Coronaviruses possess the largest known RNA genome, a 27- to 32-kb (+)-strand molecule that replicates in the cytoplasm. During virus replication, a 3' coterminal nested set of five to eight subgenomic (sg) mRNAs are made that are also 5' coterminal with the genome, because they carry the genomic leader as the result of discontinuous transcription at intergenic donor signals during (-)-strand synthesis when templates for sgmRNA synthesis are made. An unanswered question is whether the sgmRNAs, which appear rapidly and abundantly, undergo posttranscriptional amplification. Here, using RT-PCR and sequence analyses of head-to-tail-ligated (-) strands, we show that after transfection of an in vitro-generated marked sgmRNA into virus-infected cells, the sgmRNA, like the genome, can function as a template for (-)-strand synthesis. Furthermore, when the transfected sgmRNA contains an internally placed RNA-dependent RNA polymerase template-switching donor signal, discontinuous transcription occurs at this site, and a shorter, 3' terminally nested leader-containing sgmRNA is made, as evidenced by its leader-body junction and by the expression of a GFP gene. Thus, in principle, the longer-nested sgmRNAs in a natural infection, all of which contain potential internal template-switching donor signals, can function to increase the number of the shorter 3'-nested sgmRNAs. One predicted advantage of this behavior for coronavirus survivability is an increased chance of maintaining genome fitness in the 3' one-third of the genome via a homologous recombination between the (now independently abundant) WT sgmRNA and a defective genome.
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Chen SC, Olsthoorn RCL. Group-specific structural features of the 5'-proximal sequences of coronavirus genomic RNAs. Virology 2010; 401:29-41. [PMID: 20202661 PMCID: PMC7111916 DOI: 10.1016/j.virol.2010.02.007] [Citation(s) in RCA: 74] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2009] [Revised: 01/06/2010] [Accepted: 02/05/2010] [Indexed: 01/24/2023]
Abstract
Global predictions of the secondary structure of coronavirus (CoV) 5′ untranslated regions and adjacent coding sequences revealed the presence of conserved structural elements. Stem loops (SL) 1, 2, 4, and 5 were predicted in all CoVs, while the core leader transcription-regulating sequence (L-TRS) forms SL3 in only some CoVs. SL5 in group I and II CoVs, with the exception of group IIa CoVs, is characterized by the presence of a large sequence insertion capable of forming hairpins with the conserved 5′-UUYCGU-3′ loop sequence. Structure probing confirmed the existence of these hairpins in the group I Human coronavirus-229E and the group II Severe acute respiratory syndrome coronavirus (SARS-CoV). In general, the pattern of the 5′ cis-acting elements is highly related to the lineage of CoVs, including features of the conserved hairpins in SL5. The function of these conserved hairpins as a putative packaging signal is discussed.
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Affiliation(s)
- Shih-Cheng Chen
- Leiden Institute of Chemistry, Department of Molecular Genetics, Leiden University, PO Box 9502, 2300 RA Leiden, The Netherlands
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RNA Higher-Order Structures Within the Coronavirus 5′ and 3′ Untranslated Regions and Their Roles in Viral Replication. MOLECULAR BIOLOGY OF THE SARS-CORONAVIRUS 2010. [PMCID: PMC7176159 DOI: 10.1007/978-3-642-03683-5_4] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
The 5′ and 3′ untranslated regions (UTRs) of all coronaviruses contain RNA higher-order structures which play essential roles in viral transcription and replication. In this chapter we present our current knowledge of how those cis-acting elements were defined and their functional roles in viral transcription and replication. Cellular proteins which have been shown binding to those cis-acting elements and potentially support the RNA discontinuous synthesis model are also discussed. A conserved RNA structure model for the 5′ and 3′ UTRs of group 2 coronaviruses is presented with the known cellular protein binding sites.
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Liu Y, Wimmer E, Paul AV. Cis-acting RNA elements in human and animal plus-strand RNA viruses. BIOCHIMICA ET BIOPHYSICA ACTA-GENE REGULATORY MECHANISMS 2009; 1789:495-517. [PMID: 19781674 PMCID: PMC2783963 DOI: 10.1016/j.bbagrm.2009.09.007] [Citation(s) in RCA: 127] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/04/2009] [Revised: 09/09/2009] [Accepted: 09/13/2009] [Indexed: 02/08/2023]
Abstract
The RNA genomes of plus-strand RNA viruses have the ability to form secondary and higher-order structures that contribute to their stability and to their participation in inter- and intramolecular interactions. Those structures that are functionally important are called cis-acting RNA elements because their functions cannot be complemented in trans. They can be involved not only in RNA/RNA interactions but also in binding of viral and cellular proteins during the complex processes of translation, RNA replication and encapsidation. Most viral cis-acting RNA elements are located in the highly structured 5'- and 3'-nontranslated regions of the genomes but sometimes they also extend into the adjacent coding sequences. In addition, some cis-acting RNA elements are embedded within the coding sequences far away from the genomic ends. Although the functional importance of many of these structures has been confirmed by genetic and biochemical analyses, their precise roles are not yet fully understood. In this review we have summarized what is known about cis-acting RNA elements in nine families of human and animal plus-strand RNA viruses with an emphasis on the most thoroughly characterized virus families, the Picornaviridae and Flaviviridae.
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Affiliation(s)
- Ying Liu
- Department of Molecular Genetics and Microbiology, Stony Brook University, Stony Brook, NY 11790, USA
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Abstract
Viruses belonging to the family Coronaviridae are unique among RNA viruses because of the unusually large size of their genome, which is of messenger- or positive- or plus-sense. It is ∼30,000 bases or 2–3 times larger than the genomes of most other RNA viruses. Coronaviruses belong to the order Nidovirales, the other three families being the Arteriviridae, Toroviridae and Roniviridae. (For a review of classification and evolutionary relatedness of Nidovirales see Gorbalenya et al. 2006.) This grouping is based on the arrangement and relatedness of open reading frames within their genomes and on the presence in infected cells of multiple subgenomic mRNAs that form a 3'-co-terminal, nested set with the genome. Among the Nidovirales, coronaviruses (and toroviruses) are unique in their possession of a helical nucleocapsid, which is unusual for plus-stranded but not minus-stranded RNA viruses; plus-stranded RNA-containing plant viruses in the Closteroviridae and in the Tobamovirus genus also possess helical capsids. Coronaviruses are very successful and have infected many species of animals, including bats, birds (poultry) and mammals, such as humans and livestock. Coronavirus species are classified into three groups, which were based originally on cross-reacting antibodies and more recently on nucleotide sequence relatedness (Gonzalez et al. 2003). There have been several reviews of coronaviruses published recently and the reader is referred to them for more extensive references (Enjuanes et al. 2006; Masters 2006; Pasternak et al. 2006; Sawicki and Sawicki 2005; Sawicki et al. 2007; Ziebuhr 2005).
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Cao J, Wu CC, Lin TL. Complete nucleotide sequence of polyprotein gene 1 and genome organization of turkey coronavirus. Virus Res 2008; 136:43-9. [PMID: 18514348 PMCID: PMC7114415 DOI: 10.1016/j.virusres.2008.04.015] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2007] [Revised: 04/12/2008] [Accepted: 04/18/2008] [Indexed: 11/30/2022]
Abstract
The complete nucleotide sequence of polyprotein gene 1 and the assembled full-length genome sequence are presented for turkey coronavirus (TCoV) isolates 540 and ATCC. The TCoV polyprotein gene encoded two open reading frames (ORFs), which are translated into two products, pp1a and pp1ab, the latter being produced via −1 frameshift translation. TCoV polyprotein pp1a and pp1ab were predicted to be processed to 15 non-structure proteins (nsp2–nsp16), with nsp1 missing. ClustalW analysis revealed 88.99% identity and 96.99% similarity for pp1ab between TCoV and avian infectious bronchitis virus (IBV) at the amino acid level. The whole genome consists of 27,749 nucleotides for 540 and 27,816 nucleotides for ATCC, excluding the poly(A) tail. A total of 13 ORFs were predicted for TCoV. Five subgenomic RNAs were detected from ATCC-infected turkey small intestines by Northern blotting. The whole genome sequence had 86.9% identity between TCoV and IBV, supporting that TCoV is a group 3 coronavirus.
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Affiliation(s)
- Jianzhong Cao
- Department of Comparative Pathobiology, 406 South University Street, Purdue University, West Lafayette, IN 47907, USA.
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68
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Gomaa MH, Barta JR, Ojkic D, Yoo D. Complete genomic sequence of turkey coronavirus. Virus Res 2008; 135:237-46. [PMID: 18468711 PMCID: PMC7114504 DOI: 10.1016/j.virusres.2008.03.020] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2007] [Revised: 03/26/2008] [Accepted: 03/28/2008] [Indexed: 11/05/2022]
Abstract
Turkey coronavirus (TCoV), one of the least characterized of all known coronaviruses, was isolated from an outbreak of acute enteritis in young turkeys in Ontario, Canada, and the full-length genomic sequence was determined. The full-length genome was 27,632 nucleotides plus the 3′ poly(A) tail. Two open reading frames, ORFs 1a and 1b, resided in the first two thirds of the genome, and nine additional downstream ORFs were identified. A gene for hemagglutinin-esterase was absent in TCoV. The region between the membrane (M) and nucleocapsid (N) protein genes contained three potential small ORFs: ORF-X, a previously uncharacterized ORF with an associated putative TRS within the M gene (apparently shared among all group III coronaviruses), and previously described ORFs 5a and 5b. The TCoV genome is organized as follows: 5′ UTR – replicase (ORFs 1a, 1b) – spike (S) protein – ORF3 (ORFs 3a, 3b) – small envelop (E or 3c) protein – membrane (M) protein – ORF5 (ORFs X, 5a, 5b) – nucleocapsid (N) protein −3′ UTR – poly(A). TCoV genome structure and sequence was most similar, but distinct from, avian infectious bronchitis virus (IBV). This is the first complete genome sequence for a TCoV and confirms that TCoV belongs to group III coronaviruses.
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Affiliation(s)
- M H Gomaa
- Department of Pathobiology, University of Guelph, Guelph, Ontario N1G 2W1, Canada
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69
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Plant EP, Dinman JD. The role of programmed-1 ribosomal frameshifting in coronavirus propagation. FRONT BIOSCI-LANDMRK 2008; 13:4873-81. [PMID: 18508552 DOI: 10.2741/3046] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Coronaviruses have the potential to cause significant economic, agricultural and health problems. The severe acute respiratory syndrome (SARS) associated coronavirus outbreak in late 2002, early 2003 called attention to the potential damage that coronaviruses could cause in the human population. The ensuing research has enlightened many to the molecular biology of coronaviruses. A programmed -1 ribosomal frameshift is required by coronaviruses for the production of the RNA dependent RNA polymerase which in turn is essential for viral replication. The frameshifting signal encoded in the viral genome has additional features that are not essential for frameshifting. Elucidation of the differences between coronavirus frameshift signals and signals from other viruses may help our understanding of these features. Here we summarize current knowledge and add additional insight regarding the function of the programmed -1 ribosomal frameshift signal in the coronavirus lifecycle.
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Affiliation(s)
- Ewan P Plant
- Division of Emerging and Transfusion Transmitted Diseases, Center for Biologics Evaluation and Research, Food and Drug Administration, Bethesda, Maryland 20892, USA.
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70
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Genetic interactions between an essential 3' cis-acting RNA pseudoknot, replicase gene products, and the extreme 3' end of the mouse coronavirus genome. J Virol 2007; 82:1214-28. [PMID: 18032506 DOI: 10.1128/jvi.01690-07] [Citation(s) in RCA: 80] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
The upstream end of the 3' untranslated region (UTR) of the mouse hepatitis virus genome contains two essential and overlapping RNA secondary structures, a bulged stem-loop and a pseudoknot, which have been proposed to be elements of a molecular switch that is critical for viral RNA synthesis. It has previously been shown that a particular six-base insertion in loop 1 of the pseudoknot is extremely deleterious to the virus. We have now isolated multiple independent second-site revertants of the loop 1 insertion mutant, and we used reverse-genetics methods to confirm the identities of suppressor mutations that could compensate for the original insertion. The suppressors were localized to two separate regions of the genome. Members of one class of suppressor were mapped to the portions of gene 1 that encode nsp8 and nsp9, thereby providing the first evidence for specific interactions between coronavirus replicase gene products and a cis-acting genomic RNA element. The second class of suppressor was mapped to the extreme 3' end of the genome, a result which pointed to the existence of a direct base-pairing interaction between loop 1 of the pseudoknot and the genomic terminus. The latter finding was strongly supported by phylogenetic evidence and by the construction of a deletion mutant that reduced the 3' UTR to its minimal essential elements. Taken together, the interactions revealed by the two classes of suppressors suggest a model for the initiation of coronavirus negative-strand RNA synthesis.
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71
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Beerens N, Snijder EJ. An RNA pseudoknot in the 3' end of the arterivirus genome has a critical role in regulating viral RNA synthesis. J Virol 2007; 81:9426-36. [PMID: 17581985 PMCID: PMC1951461 DOI: 10.1128/jvi.00747-07] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2007] [Accepted: 06/13/2007] [Indexed: 01/06/2023] Open
Abstract
In the life cycle of plus-strand RNA viruses, the genome initially serves as the template for both translation of the viral replicase gene and synthesis of minus-strand RNA and is ultimately packaged into progeny virions. These various processes must be properly balanced to ensure efficient viral proliferation. To achieve this, higher-order RNA structures near the termini of a variety of RNA virus genomes are thought to play a key role in regulating the specificity and efficiency of viral RNA synthesis. In this study, we have analyzed the signals for minus-strand RNA synthesis in the prototype of the arterivirus family, equine arteritis virus (EAV). Using site-directed mutagenesis and an EAV reverse genetics system, we have demonstrated that a stem-loop structure near the 3' terminus of the EAV genome is required for RNA synthesis. We have also obtained evidence for an essential pseudoknot interaction between the loop region of this stem-loop structure and an upstream hairpin residing in the gene encoding the nucleocapsid protein. We propose that the formation of this pseudoknot interaction may constitute a molecular switch that could regulate the specificity or timing of viral RNA synthesis. This hypothesis is supported by the fact that phylogenetic analysis predicted the formation of similar pseudoknot interactions near the 3' end of all known arterivirus genomes, suggesting that this interaction has been conserved in evolution.
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Affiliation(s)
- Nancy Beerens
- Molecular Virology Laboratory, Department of Medical Microbiology, Leiden University Medical Center, LUMC P4-26, PO Box 9600, 2300 RC Leiden, The Netherlands
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72
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Brown CG, Nixon KS, Senanayake SD, Brian DA. An RNA stem-loop within the bovine coronavirus nsp1 coding region is a cis-acting element in defective interfering RNA replication. J Virol 2007; 81:7716-24. [PMID: 17475638 PMCID: PMC1933353 DOI: 10.1128/jvi.00549-07] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2007] [Accepted: 04/26/2007] [Indexed: 01/12/2023] Open
Abstract
Higher-order cis-acting RNA replication structures have been identified in the 3'- and 5'-terminal untranslated regions (UTRs) of a bovine coronavirus (BCoV) defective interfering (DI) RNA. The UTRs are identical to those in the viral genome, since the 2.2-kb DI RNA is composed of only the two ends of the genome fused between an internal site within the 738-nucleotide (nt) 5'-most coding region (the nsp1, or p28, coding region) and a site just 4 nt upstream of the 3'-most open reading frame (ORF) (the N gene). The joined ends of the viral genome in the DI RNA create a single continuous 1,635-nt ORF, 288 nt of which come from the 738-nt nsp1 coding region. Here, we have analyzed features of the 5'-terminal 288-nt portion of the nsp1 coding region within the continuous ORF that are required for DI RNA replication. We observed that (i) the 5'-terminal 186 nt of the nsp1 coding region are necessary and sufficient for DI RNA replication, (ii) two Mfold-predicted stem-loops within the 186-nt sequence, named SLV (nt 239 to 310) and SLVI (nt 311 to 340), are supported by RNase structure probing and by nucleotide covariation among closely related group 2 coronaviruses, and (iii) SLVI is a required higher-order structure for DI RNA replication based on mutation analyses. The function of SLV has not been evaluated. We conclude that SLVI within the BCoV nsp1 coding region is a higher-order cis-replication element for DI RNA and postulate that it functions similarly in the viral genome.
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Affiliation(s)
- Cary G Brown
- Department of Microbiology, University of Tennessee College of Veterinary Medicine, Knoxville, TN 37996-0845, USA
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