Generating in vitro transcripts with homogenous 3' ends using trans-acting antigenomic delta ribozyme

Overview of Methods for Large-Scale RNA Synthesis

In recent years, it has become clear that RNA molecules are involved in almost all vital cellular processes and pathogenesis of human disorders. The functional diversity of RNA comes from its structural richness. Although composed of only four nucleotides, RNA molecules present a plethora of secondary and tertiary structures critical for intra and intermolecular contacts with other RNAs and ligands (proteins, small metabolites, etc.). In order to fully understand RNA function it is necessary to define its spatial structure. Crystallography, nuclear magnetic resonance and cryogenic electron microscopy have demonstrated considerable success in determining the structures of biologically important RNA molecules. However, these powerful methods require large amounts of sample. Despite their limitations, chemical synthesis and in vitro transcription are usually employed to obtain milligram quantities of RNA for structural studies, delivering simple and effective methods for large-scale production of homogenous samples. The aim of this paper is to provide an overview of methods for large-scale RNA synthesis with emphasis on chemical synthesis and in vitro transcription. We also present our own results of testing the efficiency of these approaches in order to adapt the material acquisition strategy depending on the desired RNA construct.

In vitro production and multiplex quantification of 2',3'-cyclic phosphate-containing 5'-tRNA half molecules

RNA cleavages by many ribonucleases generate RNA molecules that contain a 2',3'-cyclic phosphate (cP) at their 3'-termini, and many cP-containing RNAs (cP-RNAs) are expressed as functional molecules in cells and tissues. 5'-tRNA half molecules are representative examples of functional cP-RNAs, playing important roles in various biological processes. We here show in vitro production of cP-containing 5'-tRNA half molecules that is able to prepare abundant synthetic cP-RNAs enough for functional analyses. Furthermore, we report a multiplex TaqMan RT-qPCR method which can simultaneously quantify multiple cP-containing 5'-tRNA half species. The method enabled us to efficiently quantify 5'-tRNA halves using samples with limited amounts, such as human plasma samples, revealing drastic enhancement of 5'-tRNA half levels at approximately 1,000-fold in patients infected with Mycobacterium tuberculosis. These in vitro production and multiplex quantification methods can be applied to any cP-RNAs, and they provide cost-effective, in-house techniques to accelerate expressional and functional characterizations of 5'-tRNA halves and other cP-RNAs.

A robust and versatile method for production and purification of large-scale RNA samples for structural biology

Recent findings in genome-wide transcriptomics revealed that RNAs are involved in almost every biological process, across all domains of life. The characterization of native RNAs of unknown function and structure is particularly challenging due to their typical low abundance in the cell and the inherent sensitivity toward ubiquitous RNA degrading enzymes. Therefore, robust in vitro synthesis and extensive work-up methods are often needed to obtain samples amenable for biochemical, biophysical, and structural studies. Here, we present a protocol that combines the most recent advances in T7 in vitro transcription methodology with reverse phase ion pairing and ion exchange HPLC purification of RNAs for the production of yield-optimized large-scale samples. The method is easy to follow, robust and suitable for users with little or no experience within the field of biochemistry or chromatography. The complete execution of this method, for example, for production of isotopically labeled NMR samples, can be performed in less than a week.

Reverse Genetics for Peste des Petits Ruminants Virus: Current Status and Lessons to Learn from Other Non-segmented Negative-Sense RNA Viruses

Peste des petits ruminants (PPR) is a highly contagious transboundary animal disease with a severe socio-economic impact on the livestock industry, particularly in poor countries where it is endemic. Full understanding of PPR virus (PPRV) pathobiology and molecular biology is critical for effective control and eradication of the disease. To achieve these goals, establishment of stable reverse genetics systems for PPRV would play a key role. Unfortunately, this powerful technology remains less accessible and poorly documented for PPRV. In this review, we discussed the current status of PPRV reverse genetics as well as the recent innovations and advances in the reverse genetics of other non-segmented negative-sense RNA viruses that could be applicable to PPRV. These strategies may contribute to the improvement of existing techniques and/or the development of new reverse genetics systems for PPRV.

Specific Chemical Approaches for Studying Mammalian Ribosomes Complexed with Ligands Involved in Selenoprotein Synthesis

Chemical approaches are very powerful tools for investigating the molecular structure and architecture of large ribonucleoprotein complexes involving ribosomes and other components of the translation system. Application of RNA nucleotide-specific and cross-linking reagents of a broad specificity range allows the researcher to obtain information on the sites of ligand binding to the ribosome and to each other as well as on the RNA rearrangements caused by the binding. Here, we describe specific chemical approaches including chemical probing and site-directed or bifunctional reagent-mediated cross-linking, which have been used for exploring the mechanism of selenocysteine insertion into a polypeptide chain by mammalian ribosomes.

An in-vitro transcription assay for development of Rotavirus VP7

BACKGROUND AND OBJECTIVES

Human rotavirus (RV) is responsible for most cases of acute gastroenteritis in infants, worldwide. Today, in vitro transcription (IVT) assay is widely used to develop efficient RNA for the biological experiments such as gene function analysis and reverse genetics. The aim of this study was to develop optimal full-length transcripts of the VP7 segment, using in vitro transcription assay.

MATERIALS AND METHODS

Special primers were designed in order to synthesize VP7 sequence of sense RNA in the process of IVT using T7 RNA polymerase. RT-PCR was performed using forward and reverse primers, containing T7 promoter sequence and BstUI restriction enzyme site, respectively. In order to synthesize ssRNA VP7, in accordance with the IVT technique, RV4-VP7 fragment was subcloned into PTZ57 R/T plasmid and digested by BstUI enzyme.

RESULTS

The sequencing of the VP7 gene showed 99% identity withVP7 gene of rotavirus RV4 strain (Sequence ID: M64666.1). The analysis of purity of DNA fragment and ssRNA VP7 segment revealed that OD ratio of A260/A280 and quantity of nucleic acids were (1.9, 0.036 μg/μL) and (2.02, 0.98 μg/μL), respectively.

CONCLUSION

In the present study, a modified methodology of RNA synthetase was described by IVT assay, using T7RNA polymerase in order to transcribe the full-length transcripts of human VP7-RV4 strain. This method is applicable for reverse genetic approaches, especially for the production of reassortant RV vaccine.

Synthesizing topological structures containing RNA

Though knotting and entanglement have been observed in DNA and proteins, their existence in RNA remains an enigma. Synthetic RNA topological structures are significant for understanding the physical and biological properties pertaining to RNA topology, and these properties in turn could facilitate identifying naturally occurring topologically nontrivial RNA molecules. Here we show that topological structures containing single-stranded RNA (ssRNA) free of strong base pairing interactions can be created either by configuring RNA-DNA hybrid four-way junctions or by template-directed synthesis with a single-stranded DNA (ssDNA) topological structure. By using a constructed ssRNA knot as a highly sensitive topological probe, we find that Escherichia coli DNA topoisomerase I has low RNA topoisomerase activity and that the R173A point mutation abolishes the unknotting activity for ssRNA, but not for ssDNA. Furthermore, we discover the topological inhibition of reverse transcription (RT) and obtain different RT-PCR patterns for an ssRNA knot and circle of the same sequence.

Single-Molecule Analysis of Pre-mRNA Splicing with Colocalization Single-Molecule Spectroscopy (CoSMoS)

Recent development of single-molecule techniques to study pre-mRNA splicing has provided insights into the dynamic nature of the spliceosome. Colocalization single-molecule spectroscopy (CoSMoS) allows following spliceosome assembly in real time at single-molecule resolution in the full complexity of cellular extracts. A detailed protocol of CoSMoS has been published previously (Anderson and Hoskins, Methods Mol Biol 1126:217-241, 2014). Here, we provide an update on the technical advances since the first CoSMoS studies including slide surface treatment, data processing, and representation. We describe various labeling strategies to generate RNA reporters with multiple dyes (or other moieties) at specific locations.

RNA synthesis and purification for structural studies

RNAs play pivotal roles in the cell, ranging from catalysis (e.g., RNase P), acting as adaptor molecule (tRNA) to regulation (e.g., riboswitches). Precise understanding of its three-dimensional structures has given unprecedented insight into the molecular basis for all of these processes. Nevertheless, structural studies on RNA are still limited by the very special nature of this polymer. The most common methods for the determination of 3D RNA structures are NMR and X-ray crystallography. Both methods have their own set of requirements and give different amounts of information about the target RNA. For structural studies, the major bottleneck is usually obtaining large amounts of highly pure and homogeneously folded RNA. Especially for X-ray crystallography it can be necessary to screen a large number of variants to obtain well-ordered single crystals. In this mini-review we give an overview about strategies for the design, in vitro production, and purification of RNA for structural studies.

Syn5 RNA polymerase synthesizes precise run-off RNA products

The enzyme predominantly used for in vitro run-off RNA synthesis is bacteriophage T7 RNA polymerase. T7 RNA polymerase synthesizes, in addition to run-off products of precise length, transcripts with an additional non-base-paired nucleotide at the 3′-terminus (N + 1 product). This contaminating product is extremely difficult to remove. We recently characterized the single-subunit RNA polymerase from marine cyanophage Syn5 and identified its promoter sequence. This marine enzyme catalyses RNA synthesis over a wider range of temperature and salinity than does T7 RNA polymerase. Its processivity is >30 000 nt without significant intermediate products. The requirement for the initiating nucleotide at the promoter is less stringent for Syn5 RNA polymerase as compared to T7 RNA polymerase. A major difference is the precise run-off transcripts with homogeneous 3′-termini synthesized by Syn5 RNA polymerase. Therefore, the enzyme is advantageous for the production of RNAs that require precise 3′-termini, such as tRNAs and RNA fragments that are used for subsequent assembly.

Trans-acting antigenomic HDV ribozyme for production of in vitro transcripts with homogenous 3' ends

During in vitro run-off transcription with T7 RNA polymerase, transcripts with heterogenous 3' ends are commonly synthesized. Here, we describe an efficient procedure for correct processing of transcript 3' ends with the use of antigenomic HDV ribozyme. The procedure involves the extension of nascent transcripts with seven nucleotides complementary to the ribozyme's recognition site and, subsequently, the removal of those nucleotides with the HDV ribozyme acting in trans. Sufficient reaction rates and final cleavage extents of approx. 90% can be obtained with just twofold excess of the ribozyme. The highest concentration of RNA substrate suggested for practical applications turns out to be 3 μM. The procedure is an alternative to the use of ribozymes as cis-cleaving autocatalytic cassettes attached to transcript 3' ends.

An RNA toolbox for single-molecule force spectroscopy studies

Precise, controllable single-molecule force spectroscopy studies of RNA and RNA-dependent processes have recently shed new light on the dynamics and pathways of RNA folding and RNA-enzyme interactions. A crucial component of this research is the design and assembly of an appropriate RNA construct. Such a construct is typically subject to several criteria. First, single-molecule force spectroscopy techniques often require an RNA construct that is longer than the RNA molecules used for bulk biochemical studies. Next, the incorporation of modified nucleotides into the RNA construct is required for its surface immobilization. In addition, RNA constructs for single-molecule studies are commonly assembled from different single-stranded RNA molecules, demanding good control of hybridization or ligation. Finally, precautions to prevent RNase- and divalent cation-dependent RNA digestion must be taken. The rather limited selection of molecular biology tools adapted to the manipulation of RNA molecules, as well as the sensitivity of RNA to degradation, make RNA construct preparation a challenging task. We briefly illustrate the types of single-molecule force spectroscopy experiments that can be performed on RNA, and then present an overview of the toolkit of molecular biology techniques at one's disposal for the assembly of such RNA constructs. Within this context, we evaluate the molecular biology protocols in terms of their effectiveness in producing long and stable RNA constructs.

Structural Features of Target RNA Molecules Greatly Modulate the Cleavage Efficiency of trans-Acting Delta Ribozymes

The aim of this work was to shed some more light on factors influencing the effectiveness of delta ribozyme cleavage of structured RNA molecules. An oligoribonucleotide that corresponds to the 3'-terminal region X of HCV RNA and yeast tRNAPhe were used as representative RNA targets. Only a few sites susceptible to ribozyme cleavage were identified in these targets using a combinatorial library of ribozyme variants, in which the region responsible for ribozyme-target interaction was randomized. On the other hand, the targets were fairly accessible for binding of complementary oligonucleotides, as was shown by 6-mer DNA libraries and RNase H approach. Moreover, the specifically acting ribozymes cleaved the targets precisely but with unexpectedly modest efficacy. To explain these observations, six model RNA molecules were designed, in which the same seven nucleotide long sequence recognized by the delta ribozyme was always single stranded but was embedded into different RNA structural context. These molecules were cleaved with differentiated rates, and the corresponding k2 values were in the range of 0.91-0.021 min-1; thus they differed almost 50-fold. This clearly shows that cleavage of structured RNAs might be much slower than cleavage of a short unstructured oligoribonucleotide, despite full accessibility of the targeted regions for hybridization. Restricted possibilities of conformational transitions, which are necessary to occur on the cleavage reaction trajectory, seem to be responsible for these differences. Their magnitude, which was evaluated in this work, should be taken into account while considering the use of delta ribozymes for practical applications.

Antigenomic delta ribozyme variants with mutations in the catalytic core obtained by the in vitro selection method

We have used the in vitro selection method to search for catalytically active variants of the antigenomic delta ribozyme with mutations in the regions that constitute the ribozyme active site: L3, J1/4 and J4/2. In the initial combinatorial library 16 nt positions were randomized and the library contained a full representation of all possible sequences. Following ten cycles of selection-amplification several catalytically active ribozyme variants were identified. It turned out that one-third of the variants contained only single mutation G80U and their activity was similar to that of the wild-type ribozyme. Unexpectedly, in the next one-third of the variants the C76 residue, which was proposed to play a crucial role in the ribozyme cleavage mechanism, was mutated. In these variants, however, a cytosine residue was present in a neighboring position to the polynucleotide chain. It shows that the ribozyme catalytic core possesses substantial 'structural plasticity' and the capacity of functional adaptation. Four selected ribozyme variants were subjected to more detailed analysis. It turned out that the variants differed in their relative preferences towards Mg2+, Ca2+ and Mn2+ ions. Thus, the functional properties of the variants were dependent on both the structure of their catalytic sites and divalent metal ions performing catalysis.

In vitro non-natural amino acid mutagenesis using a suppressor tRNA generated by the cis-acting hepatitis delta virus ribozyme

In vitro non-natural amino acid mutagenesis requires aminoacyl-charged suppressor transfer RNAs which read an internal stop codon. For the synthesis of aminoacyl-tRNAs loaded with non-natural amino acids, T4 RNA ligase is used to ligate a chemically synthesised aminoacyl-dinucleotide to a truncated 74mer tRNA(-CA) lacking the two 3' end nucleotides. The 74mer tRNA(-CA) in turn is generated by run-off transcription from a linearised plasmid encoding the tRNA sequence under control of the T7 promoter. Transcripts with heterogeneous ends are commonly obtained, which interfere with subsequent reactions such as ligation or translation. Here we report an improved procedure for the generation and chromatographic purification of large amounts of homogeneous 3' end tRNA(-CA) by hepatitis delta virus ribozyme cis-cleavage and the first application of this tRNA to in vitro non-natural amino acid mutagenesis. Stop codon suppression is increased compared to conventionally synthesised suppressor tRNA; 2.5 microg of mutated protein was synthesised in a 50 microl batch reaction.

A novel 4-base-recognizing RNA cutter that can remove the single 3' terminal nucleotides from RNA molecules

Mammalian tRNase ZL shows versatility in substrate recognition. This enzyme can not only process pre-tRNAs by cleaving off their 3' trailer sequences, but also recognize and cleave pre-tRNA-like complexes and micro-pre-tRNAs. Here we demonstrate that 24-27 nt hairpin RNAs (hook RNAs) can guide cleavages of separate target RNAs by tRNase ZL through the micro-pre-tRNA-like complexes between the targets and the hook RNAs and that tRNase ZL together with hook RNA works as 4-7-base-recognizing RNA cutters. The cleavage sites were located only after the nucleotide corresponding to the discriminator nucleotide. Cleavage assays for various substrate/hooker complexes showed that the cleavage efficiency changes depending on the maximum number of substrate/hooker recognition base pairings and the stem length of hook RNA and that a 5 nt recognition sequence and a hook RNA containing a 6 or 7 bp stem are the best combination for the optimal target cleavage. We also show that a 4-base RNA cutter can remove the single 3' terminal nucleotides from RNA molecules. These results indicate that this new type of RNA cutter can be utilized to homogenize at their 3' termini RNA transcripts synthesized in vitro with a bacteriophage RNA polymerase.