RNA molecules play important roles in virtually every cellular process. These functions are often mediated through the adoption of specific structures that enable RNAs to interact with other molecules. Thus, determining the secondary structures of RNAs is central to understanding their function and evolution. In recent years several sequencing-based approaches have been developed that allow probing structural features of thousands of RNA molecules present in a sample. Here, we describe nextPARS, a novel Illumina-based implementation of in vitro parallel probing of RNA structures. Our approach achieves comparable accuracy to previous implementations, while enabling higher throughput and sample multiplexing. ; This work was supported by the Spanish Ministry of Economy and Competitiveness grants "Centro de Excelencia Severo Ochoa 2013–2017" (SEV-2012-0208); the European Regional Development Fund (ERDF) from the European Union and European Research Council (ERC) Seventh Framework Programme (FP7/2007–2013) (ERC-2012-StG-310325); and the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement (H2020-MSCA-ITN-2014-642095).
Here we introduce the Computational Recognition of Secondary Structure (CROSS) method to calculate the structural profile of an RNA sequence (single- or double-stranded state) at single-nucleotide resolution and without sequence length restrictions. We trained CROSS using data from high-throughput experiments such as Selective 2΄-Hydroxyl Acylation analyzed by Primer Extension (SHAPE; Mouse and HIV transcriptomes) and Parallel Analysis of RNA Structure (PARS; Human and Yeast transcriptomes) as well as high-quality NMR/X-ray structures (PDB database). The algorithm uses primary structure information alone to predict experimental structural profiles with >80% accuracy, showing high performances on large RNAs such as Xist (17 900 nucleotides; Area Under the ROC Curve AUC of 0.75 on dimethyl sulfate (DMS) experiments). We integrated CROSS in thermodynamics-based methods to predict secondary structure and observed an increase in their predictive power by up to 30%. ; The research leading to these results has received funding from European Union Seventh Framework Programme [FP7/2007-2013]; European Research Council [RIBOMYLOME_309545 to GGT]; Spanish Ministry of Economy and Competitiveness [BFU2014-55054-P to GGT]; AGAUR [2014 SGR 00685 to GGT]; Spanish Ministry of Economy and Competitiveness, European Research Development Fund ERDF, 'Centro de Excelencia Severo Ochoa 2013-2017' [SEV-2012-0208]. Funding for open access charge: European Research Council [RIBOMYLOME_309545 to GGT]; Spanish Ministry of Economy and Competitiveness [BFU2014-55054-P to GGT]. The authors also thank the CRG fellowship to SM.
To compare the secondary structure profiles of RNA molecules we developed the CROSSalign method. CROSSalign is based on the combination of the Computational Recognition Of Secondary Structure (CROSS) algorithm to predict the RNA secondary structure profile at single-nucleotide resolution and the Dynamic Time Warping (DTW) method to align profiles of different lengths. We applied CROSSalign to investigate the structural conservation of long non-coding RNAs such as XIST and HOTAIR as well as ssRNA viruses including HIV. CROSSalign performs pair-wise comparisons and is able to find homologs between thousands of matches identifying the exact regions of similarity between profiles of different lengths. In a pool of sequences with the same secondary structure CROSSalign accurately recognizes repeat A of XIST and domain D2 of HOTAIR and outperforms other methods based on covariance modeling. The algorithm is freely available at the webpage http://service.tartaglialab.com//new_submission/crossalign. ; The research leading to these results has received funding from the European Union Seventh Framework Programme (FP7/2007–2013), through the European Research Council, under grant agreement RIBOMYLOME_309545 (Gian Gaetano Tartaglia), and from the Spanish Ministry of Economy and Competitiveness (BFU2014-55054-P and BFU2017-86970-P). We also acknowledge support from AGAUR (2014 SGR 00685), the Spanish Ministry of Economy and Competitiveness, Centro de Excelencia Severo Ochoa 2013–2017 (SEV-2012-0208). We also thank the CRG fellowship to SM.
Abstract The nucleocapsid (N) protein of SARS-CoV-2 binds viral RNA, condensing it inside the virion, and phase separating with RNA to form liquid–liquid condensates. There is little consensus on what differentiates sequence-independent N–RNA interactions in the virion or in liquid droplets from those with specific genomic RNA (gRNA) motifs necessary for viral function inside infected cells. To identify the RNA structures and the N domains responsible for specific interactions and phase separation, we use the first 1,000 nt of viral RNA and short RNA segments designed as models for single-stranded and paired RNA. Binding affinities estimated from fluorescence anisotropy of these RNAs to the two-folded domains of N (the NTD and CTD) and comparison to full-length N demonstrate that the NTD binds preferentially to single-stranded RNA, and while it is the primary RNA-binding site, it is not essential to phase separation. Nuclear magnetic resonance spectroscopy identifies two RNA-binding sites on the NTD: a previously characterized site and an additional although weaker RNA-binding face that becomes prominent when binding to the primary site is weak, such as with dsRNA or a binding-impaired mutant. Phase separation assays of nucleocapsid domains with double-stranded and single-stranded RNA structures support a model where multiple weak interactions, such as with the CTD or the NTD's secondary face promote phase separation, while strong, specific interactions do not. These studies indicate that both strong and multivalent weak N–RNA interactions underlie the multifunctional abilities of N.
Molecular beacons (MBs) are oligonucleotide probes with a hairpin-like structure that are typically labelled at the 5′ and 3′ ends with a fluorophore and a quencher dye, respectively. The conformation of the MB acts as a switch for fluorescence emission. When the fluorophore is in close proximity to the quencher, fluorescence emission cannot be detected, meaning that the switch is in an OFF state. However, if the MB structure is modified, separating the fluorophore from the quencher, the switch turns ON allowing fluorescence emission. This property has been extensively used for a wide variety of applications including real-time PCR reactions, study of protein-DNA interactions, and identification of conformational changes in RNA structures. Here, we describe a protocol based on the MB technology to measure the RNA unfolding capacities of the CspA RNA chaperone from Staphylococcus aureus. This method, with slight variations, may also be applied for testing the activity of other RNA chaperones, RNA helicases, or ribonucleases. ; This work was supported by the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (Grant Agreement No. 646869) and the Spanish Ministry of Economy and Competitiveness (BFU2014-56698-P). C.J.C. was supported by a predoctoral contract from the Public University of Navarre (UPNA), Spain.
Molecular beacons (MBs) are oligonucleotide probes with a hairpin-like structure that are typically labelled at the 5′ and 3′ ends with a fluorophore and a quencher dye, respectively. The conformation of the MB acts as a switch for fluorescence emission. When the fluorophore is in close proximity to the quencher, fluorescence emission cannot be detected, meaning that the switch is in an OFF state. However, if the MB structure is modified, separating the fluorophore from the quencher, the switch turns ON allowing fluorescence emission. This property has been extensively used for a wide variety of applications including real-time PCR reactions, study of protein-DNA interactions, and identification of conformational changes in RNA structures. Here, we describe a protocol based on the MB technology to measure the RNA unfolding capacities of the CspA RNA chaperone from Staphylococcus aureus. This method, with slight variations, may also be applied for testing the activity of other RNA chaperones, RNA helicases, or ribonucleases. ; This work was supported by the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (Grant Agreement No. 646869) and the Spanish Ministry of Economy and Competitiveness (BFU2014-56698-P). C.J.C. was supported by a predoctoral contract from the Public University of Navarre (UPNA), Spain.
MOTIVATION: RNA structure is difficult to predict in vivo due to interactions with enzymes and other molecules. Here we introduce CROSSalive, an algorithm to predict the single- and double-stranded regions of RNAs in vivo using predictions of protein interactions. RESULTS: Trained on icSHAPE data in presence (m6a+) and absence of N6 methyladenosine modification (m6a-), CROSSalive achieves cross-validation accuracies between 0.70 and 0.88 in identifying high-confidence single- and double-stranded regions. The algorithm was applied to the long non-coding RNA Xist (17 900 nt, not present in the training) and shows an Area under the ROC curve of 0.83 in predicting structured regions. AVAILABILITY AND IMPLEMENTATION: CROSSalive webserver is freely accessible at http://service.tartaglialab.com/new_submission/crossalive. SUPPLEMENTARY INFORMATION: Supplementary data are available at Bioinformatics online. ; The research leading to these results has received funding from European Research Council RIBOMYLOME_309545, European Union's Horizon 2020 IASIS_727658 and INFORE_825070, as well as Spanish Ministry of Economy and Competitiveness BFU2017-86970-P
Many biological processes are RNA-mediated, but higher-order structures for most RNAs are unknown, making it difficult to understand how RNA structure governs function. Here we describe SHAPE mutational profiling (SHAPE-MaP) that makes possible de novo and large-scale identification of RNA functional motifs. Sites of 2'-hydroxyl acylation by SHAPE are encoded as non-complementary nucleotides during cDNA synthesis, as measured by massively parallel sequencing. SHAPE-MaP-guided modeling identified greater than 90% of accepted base pairs in complex RNAs of known structure and was used to define a second-generation model for the HIV-1 RNA genome. The HIV-1 model contains all known structured motifs and previously unknown elements, including experimentally validated pseudoknots. SHAPE-MaP yields accurate and high-resolution secondary structure models, enables analysis of low abundance RNAs, disentangles sequence polymorphisms in single experiments, and will ultimately democratize RNA structure analysis.
Thermoregulation of virulence genes in bacterial pathogens is essential for environment-to-host transition. However, the mechanisms governing cold adaptation when outside the host remain poorly understood. Here, we found that the production of cold shock proteins CspB and CspC from Staphylococcus aureus is controlled by two paralogous RNA thermoswitches. Through in silico prediction, enzymatic probing and site-directed mutagenesis, we demonstrated that cspB and cspC 5′UTRs adopt alternative RNA structures that shift from one another upon temperature shifts. The open (O) conformation that facilitates mRNA translation is favoured at ambient temperatures (22°C). Conversely, the alternative locked (L) conformation, where the ribosome binding site (RBS) is sequestered in a double-stranded RNA structure, is folded at host-related temperatures (37°C). These structural rearrangements depend on a long RNA hairpin found in the O conformation that sequesters the anti-RBS sequence. Notably, the remaining S. aureus CSP, CspA, may interact with a UUUGUUU motif located in the loop of this long hairpin and favour the folding of the L conformation. This folding represses CspB and CspC production at 37°C. Simultaneous deletion of the cspB/cspC genes or their RNA thermoswitches significantly decreases S. aureus growth rate at ambient temperatures, highlighting the importance of CspB/CspC thermoregulation when S. aureus transitions from the host to the environment. ; A.T.-A. was supported by the European Research Council under the European Union's Horizon 2020 research and innovation program [ERC-CoG-2014-646869]; and the Spanish Ministry of Science and Innovation [PID2019-105216GB-I00] grants. I.C. was supported by Centre National de la Recherche Scientifique (CNRS) through an International Project of Scientific Cooperation between CNRS and CSIC [PICS07507]; and by the framework of the labEx Net RNA, French National Research Agency [ANR-10-LABX-0036 and IMCBio ANR-17-EURE-0023]. Funding for open access charge: CSIC Open Access Publication Support Initiative, Unit of Information Resources for Research (URICI).
RNA technologies are the driving forces of modern medicine and biotechnology. They combine the fields of biochemistry, chemistry, molecular biology, cell biology, physics, nanotechnology and bioinformatics. The combination of these topics is set to revolutionize the medicine of tomorrow. After more than 15 years of extensive research in the field of RNA technologies, the first therapeutics are ready to reach the first patients. Thus we are witnessing the birth of a very exciting time in the development of molecular medicine, which will be based on the methods of RNA technologies. This volume is the first of a series. It covers various aspects of RNA interference and microRNAs, although antisense RNA applications, hammerhead ribozyme structure and function as well as non-coding RNAs are also discussed. The authors are internationally highly respected experts in the field of RNA technologies.
Thosea asigna virus (TaV), an insect virus belonging to the Permutatetraviridae family, has a positive-sense single-stranded RNA (ssRNA) genome with two overlapping open reading frames, encoding for the replicase and capsid proteins. The particular TaV replicase includes a structurally unique RNA-dependent RNA polymerase (RdRP) with a sequence permutation in the palm sub-domain, where the active site is anchored. This non-canonical arrangement of the RdRP palm is also found in double-stranded RNA viruses of the Birnaviridae family. Both virus families also share a conserved VPg sequence motif at the polymerase N-terminus which in birnaviruses appears to be used to covalently link a fraction of the replicase molecules to the 5'-end of the genomic segments. Birnavirus VPgs are presumed to be used as primers for replication initiation. Here we have solved the crystal structure of the TaV RdRP, the first non-canonical RdRP of a ssRNA virus, in its apo- form and bound to different substrates. The enzyme arranges as a stable dimer maintained by mutual interactions between the active site cleft of one molecule and the flexible N-terminal tail of the symmetrically related RdRP. The latter, partially mimicking the RNA template backbone, is involved in regulating the polymerization activity. As expected from previous sequence-based bioinformatics predictions, the overall architecture of the TaV enzyme shows important resemblances with birnavirus polymerases. In addition, structural comparisons and biochemical analyses reveal unexpected similarities between the TaV RdRP and those of Flaviviruses. In particular, a long loop protruding from the thumb domain towards the central enzyme cavity appears to act as a platform for de novo initiation of RNA replication. Our findings strongly suggest an unexpected evolutionary relationship between the RdRPs encoded by these distant ssRNA virus groups. ; Work in Barcelona was supported by grant BIO2011-24333 from the Spanish Ministry of Economy and Competitiveness and by the SILVER Large Scale Collaborative Project, grant agreement number 260644, of the European Union 7th Framework. Work in Madrid was supported by grant AGL2011-24758 from the Spanish Ministry of Economy and Competitiveness. X-ray data were collected at the ESRF (Grenoble, France) within a Block Allocation Group (BAG Barcelona) and at the SLS (Villigen, Switzerland). Financial support was provided by the ESRF and SLS. DSF was supported by a pre-doctoral fellowship from fundació "La Caixa" ; Peer Reviewed
PMCID: PMC443556.-- Final edited version available at: http://dx.doi.org/10.1093/nar/gnh088 ; Many studies have tried to identify specific nucleotide sequences in the quasispecies of hepatitis C virus (HCV) that determine resistance or sensitivity to interferon (IFN) therapy, unfortunately without conclusive results. Although viral proteins represent the most evident phenotype of the virus, genomic RNA sequences determine secondary and tertiary structures which are also part of the viral phenotype and can be involved in important biological roles. In this work, a method of RNA structure analysis has been developed based on the hybridization of labelled HCV transcripts to microarrays of complementary DNA oligonucleotides. Hybridizations were carried out at non-denaturing conditions, using appropriate temperature and buffer composition to allow binding to the immobilized probes of the RNA transcript without disturbing its secondary/tertiary structural motifs. Oligonucleotides printed onto the microarray covered the entire 5' non-coding region (5'NCR), the first three-quarters of the core region, the E2–NS2 junction and the first 400 nt of the NS3 region. We document the use of this methodology to analyse the structural degree of a large region of HCV genomic RNA in two genotypes associated with different responses to IFN treatment. The results reported here show different structural degree along the genome regions analysed, and differential hybridization patterns for distinct genotypes in NS2 and NS3 HCV regions. ; M.M. was supported in part by grants DITTO-HCV QLK2-2000-0836 from the European Commission FP5 and Red Nacional de Gastroenterología y Hepatología (C03/02). The work in Hospital Vall d'Hebron was supported in part by grants SAF2000/0183 and PROFIT (FIT-010000-2003-51) from the Ministerio de Ciencia y Tecnología. The work at CAB was supported by the European Union, Instituto Nacional de Técnica Aerospacial, Ministerio de Ciencia y Tecnología and Comunidad de Madrid. ; Peer reviewed
Abstract Lloviu virus (LLOV) is a novel filovirus detected in Schreiber's bats in Europe. The isolation of the infectious LLOV from bats has raised public health concerns. However, the virological and molecular characteristics of LLOV remain largely unknown. The nucleoprotein (NP) of LLOV encapsidates the viral genomic RNA to form a helical NP-RNA complex, which acts as a scaffold for nucleocapsid formation and de novo viral RNA synthesis. In this study, using single-particle cryoelectron microscopy, we determined two structures of the LLOV NP–RNA helical complex, comprising a full-length and a C-terminally truncated NP. The two helical structures were identical, demonstrating that the N-terminal region determines the helical arrangement of the NP. The LLOV NP–RNA protomers displayed a structure similar to that in the Ebola and Marburg virus, but the spatial arrangements in the helix differed. Structure-based mutational analysis identified amino acids involved in the helical assembly and viral RNA synthesis. These structures advance our understanding of the filovirus nucleocapsid formation and provide a structural basis for the development of antifiloviral therapeutics.
This is the final version. Available from Life Science Alliance via the DOI in this record ; During mRNA localization, RNA-binding proteins interact with specific structured mRNA localization motifs. Although several such motifs have been identified, we have limited structural information on how these interact with RNA-binding proteins. Staufen proteins bind structured mRNA motifs through dsRNA-binding domains (dsRBD) and are involved in mRNA localization in Drosophila and mammals. We solved the structure of two dsRBDs of human Staufen1 in complex with a physiological dsRNA sequence. We identified interactions between the dsRBDs and the RNA sugar–phosphate backbone and direct contacts of conserved Staufen residues to RNA bases. Mutating residues mediating nonspecific backbone interactions only affected Staufen function in Drosophila when in vitro binding was severely reduced. Conversely, residues involved in base-directed interactions were required in vivo even when they minimally affected in vitro binding. Our work revealed that Staufen can read sequence features in the minor groove of dsRNA and suggests that these influence target selection in vivo. ; This project received funding from the European Research Council (ERC) under the European Union's Seventh Framework Programme (FP7/2007-2013), ERC grant agreement no. 310957, and the Deutsche Forschungsgemeinschaft (FOR2333, BO3588/2-1 to F Bono).
