An RNA model system for investigation of pseudouridine stabilization of the codon-anticodon interaction in tRNALys, tRNAHis and tRNATyr

PseU-KeMRF: A Novel Method for Identifying RNA Pseudouridine Sites

Pseudouridine is a type of abundant RNA modification that is seen in many different animals and is crucial for a variety of biological functions. Accurately identifying pseudouridine sites within the RNA sequence is vital for the subsequent study of various biological mechanisms of pseudouridine. However, the use of traditional experimental methods faces certain challenges. The development of fast and convenient computational methods is necessary to accurately identify pseudouridine sites from RNA sequence information. To address this, we introduce a novel pseudouridine site prediction model called PseU-KeMRF, which can identify pseudouridine sites in three species, H. sapiens, S. cerevisiae, and M. musculus. Through comprehensive analysis, we selected four RNA coding schemes, including binary feature, position-specific trinucleotide propensity based on single strand (PSTNPss), nucleotide chemical property (NCP) and pseudo k-tuple composition (PseKNC). Then the support vector machine-recursive feature elimination (SVM-RFE) method was used for feature selection and the feature subset was optimized. Finally, the best feature subsets are input into the kernel based on multinomial random forests (KeMRF) classifier for cross-validation and independent testing. As a new classification method, compared with the traditional random forest, KeMRF not only improves the node splitting process of decision tree construction based on multinomial distribution, but also combines the easy to interpret kernel method for prediction, which makes the classification performance better. Our results indicate superior predictive performance of PseU-KeMRF over other existing models, which can prove that PseU-KeMRF is a highly competitive predictive model that can successfully identify pseudouridine sites in RNA sequences.

Promoted Read-through and Mutation Against Pseudouridine-CMC by an Evolved Reverse Transcriptase

Pseudouridine (Ψ) is an abundant RNA chemical modification that can play critical roles in the biological functions of RNA, and RNA-therapeutic applications. Current Ψ detection methods are limited in identifying Ψs at base-resolution in U-rich sequence contexts, where Ψ occurs frequently. The N-cyclohexyl N'-(2-morpholinoethyl)carbodiimide (CMC) can selectively label Ψ in RNA by forming the CMC-Ψ adduct. Here we report that an evolved reverse transcriptase ("RT-1306") shows promoted read-through and mutation against the CMC-Ψ. The mutation signature can resolve the occurrence of Ψs within UU-containing sequences. We developed "Mut-Ψ-seq" utilizing CMC and RT-1306 for transcriptome-wide mapping of Ψ at base-resolution. The mutation signatures robustly identify reported Ψs in human rRNAs via the ROC analysis, and elongated CMC reaction duration increases the detection sensitivity of Ψ. We report a high-confidence list of Ψ sites in polyA-enriched RNAs from HEK-293T cells identified by orthogonal chemical treatments (CMC and bisulfite). The mutation signatures resolve the position of Ψ in UU-containing sequences, revealing diverse occurrence of Ψs in such sequences. This work provides new methods and datasets for biological research of Ψ, and demonstrates the potential of combining the reverse transcriptase engineering and selective chemical labeling to expand the toolkit for RNA chemical modifications studies.

Decoding the 'Fifth' Nucleotide: Impact of RNA Pseudouridylation on Gene Expression and Human Disease

Cellular RNAs, both coding and noncoding are adorned by > 100 chemical modifications, which impact various facets of RNA metabolism and gene expression. Very often derailments in these modifications are associated with a plethora of human diseases. One of the most oldest of such modification is pseudouridylation of RNA, wherein uridine is converted to a pseudouridine (Ψ) via an isomerization reaction. When discovered, Ψ was referred to as the 'fifth nucleotide' and is chemically distinct from uridine and any other known nucleotides. Experimental evidence accumulated over the past six decades, coupled together with the recent technological advances in pseudouridine detection, suggest the presence of pseudouridine on messenger RNA, as well as on diverse classes of non-coding RNA in human cells. RNA pseudouridylation has widespread effects on cellular RNA metabolism and gene expression, primarily via stabilizing RNA conformations and destabilizing interactions with RNA-binding proteins. However, much remains to be understood about the RNA targets and their recognition by the pseudouridylation machinery, the regulation of RNA pseudouridylation, and its crosstalk with other RNA modifications and gene regulatory processes. In this review, we summarize the mechanism and molecular machinery involved in depositing pseudouridine on target RNAs, molecular functions of RNA pseudouridylation, tools to detect pseudouridines, the role of RNA pseudouridylation in human diseases like cancer, and finally, the potential of pseudouridine to serve as a biomarker and as an attractive therapeutic target.

Efficient Synthetic Access to Stable Isotope Labelled Pseudouridine Phosphoramidites for RNA NMR Spectroscopy

Here we report the efficient synthetic access to 13C/15N-labelled pseudouridine phosphoramidites, which were incorporated into a binary H/ACA box guide RNA/product complex comprising 77 nucleotides (nts) in total and into a 75 nt E. coli tRNAGly. The stable isotope (SI) labelled pseudouridines were produced via a highly efficient chemo-enzymatic synthesis. 13C/15N labelled uracils were produced via chemical synthesis and enzymatically converted to pseudouridine 5'-monophosphate (ΨMP) by using YeiN, a Ψ-5'-monophosphate C-glycosidase. Removal of the 5'-phosphate group yielded the desired pseudouridine nucleoside (Ψ), which was transformed into a phosphoramidite building suitable for RNA solid phase synthesis. A Ψ -building block carrying both a 13C and a 15N label was incorporated into a product RNA and the complex formation with a 63 nt H/ACA box RNA could be observed via NMR. Furthermore, the SI labelled pseudouridine building block was used to determine imino proton bulk water exchange rates of a 75 nt E. coli tRNAGly CCmnm5U, identifying the TΨC-loop 5-methyluridine as a modifier of the exchange rates. The efficient synthetic access to SI-labelled Ψ building blocks will allow the solution and solid-state NMR spectroscopic studies of Ψ containing RNAs and will facilitate the mass spectrometric analysis of Ψ-modified nucleic acids.

Exploring the Impact of mRNA Modifications on Translation Efficiency and Immune Tolerance to Self-Antigens

Therapeutic modified mRNAs are being developed for a broad range of human diseases. However, the impact of potential miscoding of modified mRNAs on self-tolerance remains unknown. Additionally, more studies are needed to explore the effects of nucleoside alkylation on translation. While all six tested modifications are tolerated as substrates by T7 RNA polymerase and inhibited mRNA immunogenicity, the translation efficiency varied significantly depending on the type of modification. In contrast to methylation, ethylation at the N1 position of pseudouridine (Ψ) hindered translation, suggesting that the C5-C1' glycosidic bond alone is not a critical element for high translation. Inhibition of mRNA translation was also observed with 5-methoxyuridine modification. However, this inhibition was partially alleviated through the optimization of mRNA coding sequences. BALB/c mice immunized with syngeneic ψ-modified mRNA encoding for Wilms' tumor antigen-1 (WT1) developed a low but significant level of anti-WT1 IgG antibodies compared to those immunized with either unmodified or N1-methyl ψ-modified mRNA. Overall, the data indicate that adding a simple ethyl group (-CH2CH3) at the N1 position of ψ has a major negative effect on translation despite its reduced immunogenicity. Additionally, mRNA containing Ψ may alter translation fidelity at certain codons, which could lead to a breakdown of immune tolerance to self-antigens. This concern should be taken into account during gene replacement therapies, although it could benefit mRNA-based vaccines by generating a diverse repertoire of antigens.

Pseudouridine and N1-methylpseudouridine as potent nucleotide analogues for RNA therapy and vaccine development

Modified nucleosides are integral to modern drug development, serving as crucial building blocks for creating safer, more potent, and more precisely targeted therapeutic interventions. Nucleobase modifications often confer antiviral and anti-cancer activity as monomers. When incorporated into nucleic acid oligomers, they increase stability against degradation by enzymes, enhancing the drugs' lifespan within the body. Moreover, modification strategies can mitigate potential toxic effects and reduce immunogenicity, making drugs safer and better tolerated. Particularly, N1-methylpseudouridine modification improved the efficacy of the mRNA coding for spike protein of COVID-19. This became a crucial step for developing COVID-19 vaccine applied during the 2020 pandemic. This makes N1-methylpseudouridine, and its "parent" analogue pseudouridine, potent nucleotide analogues for future RNA therapy and vaccine development. This review focuses on the structure and properties of pseudouridine and N1-methylpseudouridine. RNA has a greater structural versatility, different conformation, and chemical reactivity than DNA. Watson-Crick pairing is not strictly followed by RNA that has more unusual base pairs and base-triplets. This requires detailed structural studies and structure-activity relationship analyses for RNA, also when modifications are incorporated. Recent successes in this direction are revised in this review. We describe recent successes with using pseudouridine and N1-methylpseudouridine in mRNA drug candidates. We also highlight remaining challenges that need to be solved to develop new mRNA vaccines and therapies.

Systematic Engineering of Escherichia coli for Efficient Production of Pseudouridine from Glucose and Uracil

In this study, we proposed a biological approach to efficiently produce pseudouridine (Ψ) from glucose and uracil in vivo using engineered Escherichia coli. By screening host strains and core enzymes, E. coli MG1655 overexpressing Ψ monophosphate (ΨMP) glycosidase and ΨMP phosphatase was obtained, which displayed the highest Ψ concentration. Then, optimization of the RBS sequences, enhancement of ribose 5-phosphate supply in the cells, and overexpression of the membrane transport protein UraA were investigated. Finally, fed-batch fermentation of Ψ in a 5 L fermentor can reach 27.5 g/L with a yield of 89.2 mol % toward uracil and 25.6 mol % toward glucose within 48 h, both of which are the highest to date. In addition, the Ψ product with a high purity of 99.8% can be purified from the fermentation broth after crystallization. This work provides an efficient and environmentally friendly protocol for allowing for the possibility of Ψ bioproduction on an industrial scale.

PseUpred-ELPSO Is an Ensemble Learning Predictor with Particle Swarm Optimizer for Improving the Prediction of RNA Pseudouridine Sites

RNA pseudouridine modification exists in different RNA types of many species, and it has a significant role in regulating the expression of biological processes. To understand the functional mechanisms for RNA pseudouridine sites, the accurate identification of pseudouridine sites in RNA sequences is essential. Although several fast and inexpensive computational methods have been proposed, the challenge of improving recognition accuracy and generalization still exists. This study proposed a novel ensemble predictor called PseUpred-ELPSO for improved RNA pseudouridine site prediction. After analyzing the nucleotide composition preferences between RNA pseudouridine site sequences, two feature representations were determined and fed into the stacking ensemble framework. Then, using five tree-based machine learning classifiers as base classifiers, 30-dimensional RNA profiles are constructed to represent RNA sequences, and using the PSO algorithm, the weights of the RNA profiles were searched to further enhance the representation. A logistic regression classifier was used as a meta-classifier to complete the final predictions. Compared to the most advanced predictors, the performance of PseUpred-ELPSO is superior in both cross-validation and the independent test. Based on the PseUpred-ELPSO predictor, a free and easy-to-operate web server has been established, which will be a powerful tool for pseudouridine site identification.

Interpretable Multi-Scale Deep Learning for RNA Methylation Analysis across Multiple Species

RNA modification plays a crucial role in cellular regulation. However, traditional high-throughput sequencing methods for elucidating their functional mechanisms are time-consuming and labor-intensive, despite extensive research. Moreover, existing methods often limit their focus to specific species, neglecting the simultaneous exploration of RNA modifications across diverse species. Therefore, a versatile computational approach is necessary for interpretable analysis of RNA modifications across species. A multi-scale biological language-based deep learning model is proposed for interpretable, sequential-level prediction of diverse RNA modifications. Benchmark comparisons across species demonstrate the model's superiority in predicting various RNA methylation types over current state-of-the-art methods. The cross-species validation and attention weight visualization also highlight the model's capability to capture sequential and functional semantics from genomic backgrounds. Our analysis of RNA modifications helps us find the potential existence of "biological grammars" in each modification type, which could be effective for mapping methylation-related sequential patterns and understanding the underlying biological mechanisms of RNA modifications.

Structural Mapping of the Base Stacks Containing Post-transcriptionally Modified Bases in RNA

Post-transcriptionally modified bases play vital roles in many biochemical processes involving RNA. Analysis of the non-covalent interactions associated with these bases in RNA is crucial for providing a more complete understanding of the RNA structure and function; however, the characterization of these interactions remains understudied. To address this limitation, we present a comprehensive analysis of base stacks involving all crystallographic occurrences of the most biologically relevant modified bases in a large dataset of high-resolution RNA crystal structures. This is accompanied by a geometrical classification of the stacking contacts using our established tools. Coupled with quantum chemical calculations and an analysis of the specific structural context of these stacks, this provides a map of the stacking conformations available to modified bases in RNA. Overall, our analysis is expected to facilitate structural research on altered RNA bases.

Structural and dynamic effects of pseudouridine modifications on noncanonical interactions in RNA

Pseudouridine is the most frequently naturally occurring RNA modification, found in all classes of biologically functional RNAs. Compared to uridine, pseudouridine contains an additional hydrogen bond donor group and is therefore widely regarded as a structure stabilizing modification. However, the effects of pseudouridine modifications on the structure and dynamics of RNAs have so far only been investigated in a limited number of different structural contexts. Here, we introduced pseudouridine modifications into the U-turn motif and the adjacent U:U closing base pair of the neomycin-sensing riboswitch (NSR)-an extensively characterized model system for RNA structure, ligand binding, and dynamics. We show that the effects of replacing specific uridines with pseudouridines on RNA dynamics crucially depend on the exact location of the replacement site and can range from destabilizing to locally or even globally stabilizing. By using a combination of NMR spectroscopy, MD simulations and QM calculations, we rationalize the observed effects on a structural and dynamical level. Our results will help to better understand and predict the consequences of pseudouridine modifications on the structure and function of biologically important RNAs.

Predicting Pseudouridine Sites with Porpoise

Pseudouridine is a ubiquitous RNA modification and plays a crucial role in many biological processes. However, it remains a challenging task to identify pseudouridine sites using expensive and time-consuming experimental research. To this end, we present Porpoise, a computational approach to identify pseudouridine sites from RNA sequence data. Porpoise builds on a stacking ensemble learning framework with several informative features and achieves competitive performance compared with state-of-the-art approaches. This protocol elaborates on step-by-step use and execution of the local stand-alone version and the webserver of Porpoise. In addition, we also provide a general machine learning framework that can help identify the optimal stacking ensemble learning model using different combinations of feature-based features. This general machine learning framework can facilitate users to build their pseudouridine predictors using their in-house datasets.

ZayyuNet - A Unified Deep Learning Model for the Identification of Epigenetic Modifications Using Raw Genomic Sequences

Epigenetic modifications have a vital role in gene expression and are linked to cellular processes such as differentiation, development, and tumorigenesis. Thus, the availability of reliable and accurate methods for identifying and defining these changes facilitates greater insights into the regulatory mechanisms that rely on epigenetic modifications. The current experimental methods provide a genome-wide identification of epigenetic modifications; however, they are expensive and time-consuming. To date, several machine learning methods have been proposed for identifying modifications such as DNA N6-Methyladenine (6mA), RNA N6-Methyladenosine (m6A), DNA N4-methylcytosine (4mC), and RNA pseudouridine ( Ψ). However, these methods are task-specific computational tools and require different encoding representations of DNA/RNA sequences. In this study, we propose a unified deep learning model, called ZayyuNet, for the identification of various epigenetic modifications. The proposed model is based on an architecture called, SpinalNet, inspired by the human somatosensory system that can efficiently receive large inputs and achieve better performance. The proposed model has been evaluated on various epigenetic modifications such as 6mA, m6A, 4mC, and Ψ and the results achieved outperform current state-of-the-art models. A user-friendly web server has been built and made freely available at http://nsclbio.jbnu.ac.kr/tools/ZayyuNet/.

Data-informed reparameterization of modified RNA and the effect of explicit water models: application to pseudouridine and derivatives

Pseudouridine is one of the most abundant post-transcriptional modifications in RNA. We have previously shown that the FF99-derived parameters for pseudouridine and some of its naturally occurring derivatives in the AMBER distribution either alone or in combination with the revised γ torsion parameters (parmbsc0) failed to reproduce their conformational characteristics observed experimentally (Deb et al. in J Chem Inf Model 54:1129–1142, 2014; Deb et al. in J Comput Chem 37:1576–1588, 2016; Dutta et al. in J Chem Inf Model 60:4995–5002, 2020). However, the application of the recommended bsc0 correction did lead to an improvement in the description not only of the distribution in the γ torsional space but also of the sugar pucker distributions. In an earlier study, we examined the transferability of the revised glycosidic torsion parameters (χ_IDRP) for Ψ to its derivatives. We noticed that although these parameters in combination with the AMBER FF99-derived parameters and the revised γ torsional parameters resulted in conformational properties of these residues that were in better agreement with experimental observations, the sugar pucker distributions were still not reproduced accurately. Here we report a new set of partial atomic charges for pseudouridine, 1-methylpseudouridine, 3-methylpseudouridine and 2′-O-methylpseudouridine and a new set of glycosidic torsional parameters (χ_ND) based on chosen glycosidic torsional profiles that most closely corresponded to the NMR data for conformational propensities and studied their effect on the conformational distributions using REMD simulations at the individual nucleoside level. We have also studied the effect of the choice of water model on the conformational characteristics of these modified nucleosides. Our observations suggest that the current revised set of parameters and partial atomic charges describe the sugar pucker distributions for these residues more accurately and that the choice of a suitable water model is important for the accurate description of their conformational properties. We have further validated the revised sets of parameters by studying the effect of substitution of uridine with pseudouridine within single stranded RNA oligonucleotides on their conformational and hydration characteristics.

Challenges with Simulating Modified RNA: Insights into Role and Reciprocity of Experimental and Computational Approaches

RNA is critical to a broad spectrum of biological and viral processes. This functional diversity is a result of their dynamic nature; the variety of three-dimensional structures that they can fold into; and a host of post-transcriptional chemical modifications. While there are many experimental techniques to study the structural dynamics of biomolecules, molecular dynamics simulations (MDS) play a significant role in complementing experimental data and providing mechanistic insights. The accuracy of the results obtained from MDS is determined by the underlying physical models i.e., the force-fields, that steer the simulations. Though RNA force-fields have received a lot of attention in the last decade, they still lag compared to their protein counterparts. The chemical diversity imparted by the RNA modifications adds another layer of complexity to an already challenging problem. Insight into the effect of RNA modifications upon RNA folding and dynamics is lacking due to the insufficiency or absence of relevant experimental data. This review provides an overview of the state of MDS of modified RNA, focusing on the challenges in parameterization of RNA modifications as well as insights into relevant reference experiments necessary for their calibration.

Increased Photostability of the Integral mRNA Vaccine Component N1 -Methylpseudouridine Compared to Uridine

N1 -Methylation of pseudouridine (m1 ψ) replaces uridine (Urd) in several therapeutics, including the Moderna and BioNTech-Pfizer COVID-19 vaccines. Importantly, however, it is currently unknown if exposure to electromagnetic radiation can affect the chemical integrity and intrinsic stability of m1 ψ. In this study, the photochemistry of m1 ψ is compared to that of uridine by using photoirradiation at 267 nm, steady-state spectroscopy, and quantum-chemical calculations. Furthermore, femtosecond transient absorption measurements are collected to delineate the electronic relaxation mechanisms for both nucleosides under physiologically relevant conditions. It is shown that m1 ψ exhibits a 12-fold longer 1 ππ* decay lifetime than uridine and a 5-fold higher fluorescence yield. Notably, however, the experimental results also demonstrate that most of the excited state population in both molecules decays back to the ground state in an ultrafast time scale and that m1 ψ is 6.7-fold more photostable than Urd following irradiation at 267 nm.

Gene Expression-Based Predication of RNA Pseudouridine Modification in Tumor Microenvironment and Prognosis of Glioma Patients

Aberrant expression of methyltransferases and demethylases may augment tumor initiation, proliferation and metastasis through RNA modification, such as m⁶A and m⁵C. However, activity of pseudouridine (Ψ) modification of RNA remains unknown in glioma, the most common malignant intracranial tumor. In this study, we explored the expression profiles of the Ψ synthase genes in glioma and constructed an efficient prediction model for glioma prognosis based on the CGGA and TCGA datasets. In addition, the risk-score signature was positively associated with malignancy of gliomas and the abundance of tumor-infiltrating immune cells such as macrophages M0 and regulatory T cells (Tregs), but negatively associated with the abundance of monocytes, NK cell activation and T cell CD4⁺ naive. In terms of mechanism, the risk-score signature was positively associated with the expression of inflammatory molecules such as S100A11 and CASP4 in glioma. Overall, this study provided evidence for the activity of RNA Ψ modification in glioma malignancy and local immunity.

A Feature Fusion Predictor for RNA Pseudouridine Sites with Particle Swarm Optimizer Based Feature Selection and Ensemble Learning Approach

RNA pseudouridine modification is particularly important in a variety of cellular biological and physiological processes. It plays a significant role in understanding RNA functions, RNA structure stabilization, translation processes, etc. To understand its functional mechanisms, it is necessary to accurately identify pseudouridine sites in RNA sequences. Although some computational methods have been proposed for the identification of pseudouridine sites, it is still a challenge to improve the identification accuracy and generalization ability. To address this challenge, a novel feature fusion predictor, named PsoEL-PseU, is proposed for the prediction of pseudouridine sites. Firstly, this study systematically and comprehensively explored different types of feature descriptors and determined six feature descriptors with various properties. To improve the feature representation ability, a binary particle swarm optimizer was used to capture the optimal feature subset for six feature descriptors. Secondly, six individual predictors were trained by using the six optimal feature subsets. Finally, to fuse the effects of all six features, six individual predictors were fused into an ensemble predictor by a parallel fusion strategy. Ten-fold cross-validation on three benchmark datasets indicated that the PsoEL-PseU predictor significantly outperformed the current state-of-the-art predictors. Additionally, the new predictor achieved better accuracy in the independent dataset evaluation-accuracy which is significantly higher than that of its existing counterparts-and the user-friendly webserver developed by the PsoEL-PseU predictor has been made freely accessible.

The Importance of the Epi-Transcriptome in Translation Fidelity

RNA modifications play an essential role in determining RNA fate. Recent studies have revealed the effects of such modifications on all steps of RNA metabolism. These modifications range from the addition of simple groups, such as methyl groups, to the addition of highly complex structures, such as sugars. Their consequences for translation fidelity are not always well documented. Unlike the well-known m6A modification, they are thought to have direct effects on either the folding of the molecule or the ability of tRNAs to bind their codons. Here we describe how modifications found in tRNAs anticodon-loop, rRNA, and mRNA can affect translation fidelity, and how approaches based on direct manipulations of the level of RNA modification could potentially be used to modulate translation for the treatment of human genetic diseases.

Porpoise: a new approach for accurate prediction of RNA pseudouridine sites

Pseudouridine is a ubiquitous RNA modification type present in eukaryotes and prokaryotes, which plays a vital role in various biological processes. Almost all kinds of RNAs are subject to this modification. However, it remains a great challenge to identify pseudouridine sites via experimental approaches, requiring expensive and time-consuming experimental research. Therefore, computational approaches that can be used to perform accurate in silico identification of pseudouridine sites from the large amount of RNA sequence data are highly desirable and can aid in the functional elucidation of this critical modification. Here, we propose a new computational approach, termed Porpoise, to accurately identify pseudouridine sites from RNA sequence data. Porpoise builds upon a comprehensive evaluation of 18 frequently used feature encoding schemes based on the selection of four types of features, including binary features, pseudo k-tuple composition, nucleotide chemical property and position-specific trinucleotide propensity based on single-strand (PSTNPss). The selected features are fed into the stacked ensemble learning framework to enable the construction of an effective stacked model. Both cross-validation tests on the benchmark dataset and independent tests show that Porpoise achieves superior predictive performance than several state-of-the-art approaches. The application of model interpretation tools demonstrates the importance of PSTNPs for the performance of the trained models. This new method is anticipated to facilitate community-wide efforts to identify putative pseudouridine sites and formulate novel testable biological hypothesis.

Identification of RNA pseudouridine sites using deep learning approaches

Pseudouridine(Ψ) is widely popular among various RNA modifications which have been confirmed to occur in rRNA, mRNA, tRNA, and nuclear/nucleolar RNA. Hence, identifying them has vital significance in academic research, drug development and gene therapies. Several laboratory techniques for Ψ identification have been introduced over the years. Although these techniques produce satisfactory results, they are costly, time-consuming and requires skilled experience. As the lengths of RNA sequences are getting longer day by day, an efficient method for identifying pseudouridine sites using computational approaches is very important. In this paper, we proposed a multi-channel convolution neural network using binary encoding. We employed k-fold cross-validation and grid search to tune the hyperparameters. We evaluated its performance in the independent datasets and found promising results. The results proved that our method can be used to identify pseudouridine sites for associated purposes. We have also implemented an easily accessible web server at http://103.99.176.239/ipseumulticnn/.

Molecular Dynamics Simulation of the Conformational Preferences of Pseudouridine Derivatives: Improving the Distribution in the Glycosidic Torsion Space

There are only four derivatives of pseudouridine (Ψ) that are known to occur naturally in RNA as post-transcriptional modifications. We have studied the conformational consequences of pseudouridylation and further modifications using replica exchange molecular dynamics simulations at the nucleoside level, and the simulated conformational preferences were compared with the available experimental (NMR) data. We found that the existing AMBER FF99-derived parameters for these nucleosides did not reproduce the observed experimental features and while the recommended bsc0 correction could be combined with these parameters leading to an improvement in the description of sugar pucker distributions, the χ_OL3 correction could not be applied to these nucleosides as such because of base isomerization. On the other hand, the revised χ torsion parameters (χ_IDRP) for Ψ developed earlier by us (Deb, I., J. Comput. Chem., 2016, 37, 1576-1588) in combination with the AMBER provided parameters and the revised γ torsion parameters generated conformational distributions, which generally were in better agreement with the experimental data. A significant shift of the distribution of base orientation toward the syn conformation was observed with our revised parameter sets compared to the large excess of anti conformation predicted by the FF99 parameters. Overall, our observations indicated that our revised set of parameters (χ_IDRP) for Ψ were also able to generate conformational distributions for all of the derivatives of Ψ in better agreement with the experimental data.

Analysis and Comparison of RNA Pseudouridine Site Prediction Tools

Background:

Pseudouridine (Ψ) is the most abundant RNA modification and has important functions in a series of biological and cellular processes. Although experimental techniques have made great contributions to identify Ψ sites, they are still labor-intensive and costineffective. In the past few years, a series of computational approaches have been developed, which provided rapid and efficient approaches to identify Ψ sites.

Results:

To provide the readership with a clear landscape about the recent development in this important area, in this review, we summarized and compared the representative computational approaches developed for identifying Ψ sites. Moreover, future directions in computationally identifying Ψ sites were discussed as well.

Conclusion:

We anticipate that this review will provide novel insights into the researches on pseudouridine modification.

iPseU-NCP: Identifying RNA pseudouridine sites using random forest and NCP-encoded features

Background

Pseudouridine modification is most commonly found among various kinds of RNA modification occurred in both prokaryotes and eukaryotes. This biochemical event has been proved to occur in multiple types of RNAs, including rRNA, mRNA, tRNA, and nuclear/nucleolar RNA. Hence, gaining a holistic understanding of pseudouridine modification can contribute to the development of drug discovery and gene therapies. Although some laboratory techniques have come up with moderately good outcomes in pseudouridine identification, they are costly and required skilled work experience. We propose iPseU-NCP – an efficient computational framework to predict pseudouridine sites using the Random Forest (RF) algorithm combined with nucleotide chemical properties (NCP) generated from RNA sequences. The benchmark dataset collected from Chen et al. (2016) was used to develop iPseU-NCP and fairly compare its performances with other methods.

Results

Under the same experimental settings, comparing with three state-of-the-art methods including iPseU-CNN, PseUI, and iRNA-PseU, the Matthew’s correlation coefficient (MCC) of our model increased by about 20.0%, 55.0%, and 109.0% when tested on the H. sapiens (H_200) dataset and by about 6.5%, 35.0%, and 150.0% when tested on the S. cerevisiae (S_200) dataset, respectively. This significant growth in MCC is very important since it ensures the stability and performance of our model. With those two independent test datasets, our model also presented higher accuracy with a success rate boosted by 7.0%, 13.0%, and 20.0% and 2.0%, 9.5%, and 25.0% when compared to iPseU-CNN, PseUI, and iRNA-PseU, respectively. For majority of other evaluation metrics, iPseU-NCP demonstrated superior performance as well.

Conclusions

iPseU-NCP combining the RF and NPC-encoded features showed better performances than other existing state-of-the-art methods in the identification of pseudouridine sites. This also shows an optimistic view in addressing biological issues related to human diseases.

Computational and NMR studies of RNA duplexes with an internal pseudouridine-adenosine base pair

Pseudouridine (Ψ) is the most common chemical modification present in RNA. In general, Ψ increases the thermodynamic stability of RNA. However, the degree of stabilization depends on the sequence and structural context. To explain experimentally observed sequence dependence of the effect of Ψ on the thermodynamic stability of RNA duplexes, we investigated the structure, dynamics and hydration of RNA duplexes with an internal Ψ-A base pair in different nearest-neighbor sequence contexts. The structures of two RNA duplexes containing 5′-GΨC/3′-CAG and 5′-CΨG/3′-GAC motifs were determined using NMR spectroscopy. To gain insight into the effect of Ψ on duplex dynamics and hydration, we performed molecular dynamics (MD) simulations of RNA duplexes with 5′-GΨC/3′-CAG, 5′-CΨG/3′-GAC, 5′-AΨU/3′-UAA and 5′-UΨA/3′-AAU motifs and their unmodified counterparts. Our results showed a subtle impact from Ψ modification on the structure and dynamics of the RNA duplexes studied. The MD simulations confirmed the change in hydration pattern when U is replaced with Ψ. Quantum chemical calculations showed that the replacement of U with Ψ affected the intrinsic stacking energies at the base pair steps depending on the sequence context. The calculated intrinsic stacking energies help to explain the experimentally observed sequence dependent changes in the duplex stability from Ψ modification.

The chemical diversity of RNA modifications

Nucleic acid modifications in DNA and RNA ubiquitously exist among all the three kingdoms of life. This trait significantly broadens the genome diversity and works as an important means of gene transcription regulation. Although mammalian systems have limited types of DNA modifications, over 150 different RNA modification types have been identified, with a wide variety of chemical diversities. Most modifications occur on transfer RNA and ribosomal RNA, however many of the modifications also occur on other types of RNA species including mammalian mRNA and small nuclear RNA, where they are essential for many biological roles, including developmental processes and stem cell differentiation. These post-transcriptional modifications are enzymatically installed and removed in a site-specific manner by writer and eraser proteins respectively, while reader proteins can interpret modifications and transduce the signal for downstream functions. Dysregulation of mRNA modifications manifests as disease states, including multiple types of human cancer. In this review, we will introduce the chemical features and biological functions of these modifications in the coding and non-coding RNA species.

iPseU-CNN: Identifying RNA Pseudouridine Sites Using Convolutional Neural Networks

Pseudouridine is the most prevalent RNA modification and has been found in both eukaryotes and prokaryotes. Currently, pseudouridine has been demonstrated in several kinds of RNAs, such as small nuclear RNA, rRNA, tRNA, mRNA, and small nucleolar RNA. Therefore, its significance to academic research and drug development is understandable. Through biochemical experiments, the pseudouridine site identification has produced good outcomes, but these lab exploratory methods and biochemical processes are expensive and time consuming. Therefore, it is important to introduce efficient methods for identification of pseudouridine sites. In this study, an intelligent method for pseudouridine sites using the deep-learning approach was developed. The proposed prediction model is called iPseU-CNN (identifying pseudouridine by convolutional neural networks). The existing methods used handcrafted features and machine-learning approaches to identify pseudouridine sites. However, the proposed predictor extracts the features of the pseudouridine sites automatically using a convolution neural network model. The iPseU-CNN model yields better outcomes than the current state-of-the-art models in all evaluation parameters. It is thus highly projected that the iPseU-CNN predictor will become a helpful tool for academic research on pseudouridine site prediction of RNA, as well as in drug discovery.

The emerging impact of tRNA modifications in the brain and nervous system

A remarkable number of neurodevelopmental disorders have been linked to defects in tRNA modifications. These discoveries place tRNA modifications in the spotlight as critical modulators of gene expression pathways that are required for proper organismal growth and development. Here, we discuss the emerging molecular and cellular functions of the diverse tRNA modifications linked to cognitive and neurological disorders. In particular, we describe how the structure and location of a tRNA modification influences tRNA folding, stability, and function. We then highlight how modifications in tRNA can impact multiple aspects of protein translation that are instrumental for maintaining proper cellular proteostasis. Importantly, we describe how perturbations in tRNA modification lead to a spectrum of deleterious biological outcomes that can disturb neurodevelopment and neurological function. Finally, we summarize the biological themes shared by the different tRNA modifications linked to cognitive disorders and offer insight into the future questions that remain to decipher the role of tRNA modifications. This article is part of a Special Issue entitled: mRNA modifications in gene expression control edited by Dr. Soller Matthias and Dr. Fray Rupert.

RNAs, Phase Separation, and Membrane-Less Organelles: Are Post-Transcriptional Modifications Modulating Organelle Dynamics?

Membranous organelles allow sub-compartmentalization of biological processes. However, additional subcellular structures create dynamic reaction spaces without the need for membranes. Such membrane-less organelles (MLOs) are physiologically relevant and impact development, gene expression regulation, and cellular stress responses. The phenomenon resulting in the formation of MLOs is called liquid-liquid phase separation (LLPS), and is primarily governed by the interactions of multi-domain proteins or proteins harboring intrinsically disordered regions as well as RNA-binding domains. Although the presence of RNAs affects the formation and dissolution of MLOs, it remains unclear how the properties of RNAs exactly contribute to these effects. Here, the authors review this emerging field, and explore how particular RNA properties can affect LLPS and the behavior of MLOs. It is suggested that post-transcriptional RNA modification systems could be contributors for dynamically modulating the assembly and dissolution of MLOs.

Simulation study of the ability of a computationally-designed peptide to recognize target tRNALys3 and other decoy tRNAs

In this paper, we investigate the ability of our computationally-designed peptide, Pept10 (PNWNGNRWLNNCLRG), to recognize the anticodon stem and loop (ASL) domain of the hypermodified tRNA^Lys3 (mcm⁵ s² U₃₄ ,ms² t⁶ A₃₇ ), a reverse transcription primer of HIV replication. Five other ASLs, the singly modified ASL^Lys3 (ms² t⁶ A₃₇ ), ASL^Lys3 (s² U₃₄ ), ASL^Lys3 (Ψ₃₉ ), ASL^Lys1,2 (t⁶ A₃₇ ), and ASL^Glu (s² U₃₄ ), were used as decoys. Explicit-solvent atomistic molecular dynamics simulations were performed to examine the process of binding of Pept10 with the target ASL^Lys3 (mcm⁵ s² U₃₄ ,ms² t⁶ A₃₇ ) and the decoy ASLs. Simulation results demonstrated that Pept10 is capable of recognizing the target ASL^Lys3 (mcm⁵ s² U₃₄ ,ms² t⁶ A₃₇ ) as well as one of the decoys, ASL^Lys3 (Ψ₃₉ ), but screens out the other four decoy ASLs. The interchain van der Waals (VDW) and charge-charge (ELE + EGB) energies for the two best complexes were evaluated to shed light on the molecular recognition mechanism between Pept10 and ASLs. The results indicated that Pept10 recognizes and binds to the target ASL^Lys3 (mcm⁵ s² U₃₄ ,ms² t⁶ A₃₇ ) through residues W₃ and R₇ which interact with the nucleotides mcm⁵ s² U₃₄ , U₃₅ , and ms² t⁶ A₃₇ via the interchain VDW energy. Pept10 also recognizes the decoy ASL^Lys3 (Ψ₃₉ ) through residue R₁₄ which contacts the nucleotide U₃₆ via the interchain VDW energy. Regardless of the type of ASL, the positively charged arginines on Pept10 are attracted to the negatively charged phosphate linkages on the ASL via the interchain ELE + EGB energy, thereby enhancing the binding affinity.

Pseudouridine in the Anticodon of Escherichia coli tRNATyr(QΨA) Is Catalyzed by the Dual Specificity Enzyme RluF

Pseudouridine is found in almost all cellular ribonucleic acids (RNAs). Of the multiple characteristics attributed to pseudouridine, making messenger RNAs (mRNAs) highly translatable and non-immunogenic is one such feature that directly implicates this modification in protein synthesis. We report the existence of pseudouridine in the anticodon of Escherichia coli tyrosine transfer RNAs (tRNAs) at position 35. Pseudouridine was verified by multiple detection methods, which include pseudouridine-specific chemical derivatization and gas phase dissociation of RNA during liquid chromatography tandem mass spectrometry (LC-MS/MS). Analysis of total tRNA isolated from E. coli pseudouridine synthase knock-out mutants identified RluF as the enzyme responsible for this modification. Furthermore, the absence of this modification compromises the translational ability of a luciferase reporter gene coding sequence when it is preceded by multiple tyrosine codons. This effect has implications for the translation of mRNAs that are rich in tyrosine codons in bacterial expression systems.

Pseudouridine: the fifth RNA nucleotide with renewed interests

More than 100 different types of chemical modifications to RNA have been documented so far. Historically, most of these modifications were found in rRNA, tRNA and snRNA; recently, new methods aided by high-throughput sequencing have enabled identification of chemical modifications to mRNA, leading to the emerging field of 'RNA epigenetics'. One such example is pseudouridine, which has long been known as a RNA modification in abundant non-coding RNA (ncRNA) and has recently been found to be present in mRNAas well. This review first summarizes biogenesis and known functions of pseudouridine in ncRNAs. We then focus on progress in pseudouridine detection, especially the chemical-assisted, transcriptome-wide sequencing tools that revealed the dynamic nature of mRNA pseudouridylation. Such enabling tools are expected to facilitate future functional studies of pseudouridine.

Structural effects of modified ribonucleotides and magnesium in transfer RNAs

Modified nucleotides are ubiquitous and important to tRNA structure and function. To understand their effect on tRNA conformation, we performed a series of molecular dynamics simulations on yeast tRNA^Phe and tRNA_init, Escherichia coli tRNA_init and HIV tRNA^Lys. Simulations were performed with the wild type modified nucleotides, using the recently developed CHARMM compatible force field parameter set for modified nucleotides (J. Comput. Chem.2016, 37, 896), or with the corresponding unmodified nucleotides, and in the presence or absence of Mg²⁺. Results showed a stabilizing effect associated with the presence of the modifications and Mg²⁺ for some important positions, such as modified guanosine in position 37 and dihydrouridines in 16/17 including both structural properties and base interactions. Some other modifications were also found to make subtle contributions to the structural properties of local domains. While we were not able to investigate the effect of adenosine 37 in tRNA_init and limitations were observed in the conformation of E. coli tRNA_init, the presence of the modified nucleotides and of Mg²⁺ better maintained the structural features and base interactions of the tRNA systems than in their absence indicating the utility of incorporating the modified nucleotides in simulations of tRNA and other RNAs.

Comparative Structural Dynamics of tRNA(Phe) with Respect to Hinge Region Methylated Guanosine: A Computational Approach

Transfer RNAs (tRNAs) contain various uniquely modified nucleosides thought to be useful for maintaining the structural stability of tRNAs. However, their significance for upholding the tRNA structure has not been investigated in detail at the atomic level. In this study, molecular dynamic simulations have been performed to assess the effects of methylated nucleic acid bases, N (2)-methylguanosine (m(2)G) and N (2)-N (2)-dimethylguanosine (m 2 (2) G) at position 26, i.e., the hinge region of E. coli tRNA(Phe) on its structure and dynamics. The results revealed that tRNA(Phe) having unmodified guanosine in the hinge region (G26) shows structural rearrangement in the core of the molecule, resulting in lack of base stacking interactions, U-turn feature of the anticodon loop, and TΨC loop. We show that in the presence of the unmodified guanosine, the overall fold of tRNA(Phe) is essentially not the same as that of m(2)G26 and m 2 (2) G26 containing tRNA(Phe). This structural rearrangement arises due to intrinsic factors associated with the weak hydrogen-bonding patterns observed in the base triples of the tRNA(Phe) molecule. The m(2)G26 and m 2 (2) G26 containing tRNA(Phe) retain proper three-dimensional fold through tertiary interactions. Single-point energy and molecular electrostatics potential calculation studies confirmed the structural significance of tRNAs containing m(2)G26 and m 2 (2) G26 compared to tRNA with normal G26, showing that the mono-methylated (m(2)G26) and dimethylated (m 2 (2) G26) modifications are required to provide structural stability not only in the hinge region but also in the other parts of tRNA(Phe). Thus, the present study allows us to better understand the effects of modified nucleosides and ionic environment on tRNA folding.

Pseudouridine synthase 1 deficient mice, a model for Mitochondrial Myopathy with Sideroblastic Anemia, exhibit muscle morphology and physiology alterations

Mitochondrial myopathy with lactic acidosis and sideroblastic anemia (MLASA) is an oxidative phosphorylation disorder, with primary clinical manifestations of myopathic exercise intolerance and a macrocytic sideroblastic anemia. One cause of MLASA is recessive mutations in PUS1, which encodes pseudouridine (Ψ) synthase 1 (Pus1p). Here we describe a mouse model of MLASA due to mutations in PUS1. As expected, certain Ψ modifications were missing in cytoplasmic and mitochondrial tRNAs from Pus1^−/− animals. Pus1^−/− mice were born at the expected Mendelian frequency and were non-dysmorphic. At 14 weeks the mutants displayed reduced exercise capacity. Examination of tibialis anterior (TA) muscle morphology and histochemistry demonstrated an increase in the cross sectional area and proportion of myosin heavy chain (MHC) IIB and low succinate dehydrogenase (SDH) expressing myofibers, without a change in the size of MHC IIA positive or high SDH myofibers. Cytochrome c oxidase activity was significantly reduced in extracts from red gastrocnemius muscle from Pus1^−/− mice. Transmission electron microscopy on red gastrocnemius muscle demonstrated that Pus1^−/− mice also had lower intermyofibrillar mitochondrial density and smaller mitochondria. Collectively, these results suggest that alterations in muscle metabolism related to mitochondrial content and oxidative capacity may account for the reduced exercise capacity in Pus1^−/− mice.

Rapid and dynamic transcriptome regulation by RNA editing and RNA modifications

Advances in next-generation sequencing and mass spectrometry have revealed widespread messenger RNA modifications and RNA editing, with dramatic effects on mammalian transcriptomes. Factors introducing, deleting, or interpreting specific modifications have been identified, and analogous with epigenetic terminology, have been designated "writers," "erasers," and "readers." Such modifications in the transcriptome are referred to as epitranscriptomic changes and represent a fascinating new layer of gene expression regulation that has only recently been appreciated. Here, we outline how RNA editing and RNA modification can rapidly affect gene expression, making both processes as well suited to respond to cellular stress and to regulate the transcriptome during development or circadian periods.

Additive CHARMM force field for naturally occurring modified ribonucleotides

More than 100 naturally occurring modified nucleotides have been found in RNA molecules, in particular in tRNAs. We have determined molecular mechanics force field parameters compatible with the CHARMM36 all‐atom additive force field for all these modifications using the CHARMM force field parametrization strategy. Emphasis was placed on fine tuning of the partial atomic charges and torsion angle parameters. Quantum mechanics calculations on model compounds provided the initial set of target data, and extensive molecular dynamics simulations of nucleotides and oligonucleotides in aqueous solutions were used for further refinement against experimental data. The presented parameters will allow for computational studies of a wide range of RNAs containing modified nucleotides, including the ribosome and transfer RNAs. © 2016 The Authors. Journal of Computational Chemistry Published by Wiley Periodicals, Inc.

Modified Nucleosides of Escherichia coli Ribosomal RNA

The modified nucleosides of RNA are chemically altered versions of the standard A, G, U, and C nucleosides. This review reviews the nature and location of the modified nucleosides of Escherichia coli rRNA, the enzymes that form them, and their known and/or putative functional role. There are seven Ψ (pseudouridines) synthases to make the 11 pseudouridines in rRNA. There is disparity in numbers because RluC and RluD each make 3 pseudouridines. Crystal structures have shown that the Ψ synthase domain is a conserved fold found only in all five families of Ψ synthases. The conversion of uridine to Ψ has no precedent in known metabolic reactions. Other enzymes are known to cleave the glycosyl bond but none carry out rotation of the base and rejoining to the ribose while still enzyme bound. Ten methyltransferases (MTs) are needed to make all the methylated nucleosides in 16S RNA, and 14 are needed for 23S RNA. Biochemical studies indicate that the modes of substrate recognition are idiosyncratic for each Ψ synthase since no common mode of recognition has been detected in studies of the seven synthases. Eight of the 24 expected MTs have been identified, and six crystal structures have been determined. Seven of the MTs and five of the structures are class I MTs with the appropriate protein fold plus unique appendages for the Ψ synthases. The remaining MT, RlmB, has the class IV trefoil knot fold.

Accurate placement of substrate RNA by Gar1 in H/ACA RNA-guided pseudouridylation

H/ACA RNA-guided ribonucleoprotein particle (RNP), the most complicated RNA pseudouridylase so far known, uses H/ACA guide RNA for substrate capture and four proteins (Cbf5, Nop10, L7Ae and Gar1) for pseudouridylation. Although it was shown that Gar1 not only facilitates the product release, but also enhances the catalytic activity, the chemical role that Gar1 plays in this complicated machinery is largely unknown. Kinetics measurement on Pyrococcus furiosus RNPs at different temperatures making use of fluorescence anisotropy showed that Gar1 reduces the catalytic barrier through affecting the activation entropy instead of enthalpy. Site-directed mutagenesis combined with molecular dynamics simulations demonstrated that V149 in the thumb loop of Cbf5 is critical in placing the target uridine to the right position toward catalytic D85 of Cbf5. The enzyme elegantly aligns the position of uridine in the catalytic site with the help of Gar1. In addition, conversion of uridine to pseudouridine results in a rigid syn configuration of the target nucleotide in the active site and causes Gar1 to pull out the thumb. Both factors guarantee the efficient release of the product.

Pseudouridine profiling reveals regulated mRNA pseudouridylation in yeast and human cells

Post-transcriptional modification of RNA nucleosides occurs in all living organisms. Pseudouridine, the most abundant modified nucleoside in non-coding RNAs¹, enhances the function of transfer RNA and ribosomal RNA by stabilizing RNA structure^2–8. mRNAs were not known to contain pseudouridine, but artificial pseudouridylation dramatically affects mRNA function – it changes the genetic code by facilitating non-canonical base pairing in the ribosome decoding center^9,10. However, without evidence of naturally occurring mRNA pseudouridylation, its physiological was unclear. Here we present a comprehensive analysis of pseudouridylation in yeast and human RNAs using Pseudo-seq, a genome-wide, single-nucleotide-resolution method for pseudouridine identification. Pseudo-seq accurately identifies known modification sites as well as 100 novel sites in non-coding RNAs, and reveals hundreds of pseudouridylated sites in mRNAs. Genetic analysis allowed us to assign most of the new modification sites to one of seven conserved pseudouridine synthases, Pus1–4, 6, 7 and 9. Notably, the majority of pseudouridines in mRNA are regulated in response to environmental signals, such as nutrient deprivation in yeast and serum starvation in human cells. These results suggest a mechanism for the rapid and regulated rewiring of the genetic code through inducible mRNA modifications. Our findings reveal unanticipated roles for pseudouridylation and provide a resource for identifying the targets of pseudouridine synthases implicated in human disease^11–13.

Conformational preferences of modified uridines: comparison of AMBER derived force fields

The widespread occurrence of modified residues in RNA sequences necessitates development of accurate parameters for these modifications for reliable modeling of RNA structure and dynamics. A comprehensive set of parameters for the 107 naturally occurring RNA modifications was proposed by Aduri et al. (J. Chem. Theory Comput. 2007, 3, 1464-1475) for the AMBER FF99 force field. In this work, we tested these parameters on a set of modified uridine residues, namely, dihydrouridine, 2-thiouridine, 4-thiouridine, pseudouridine, and uridine-5-oxyacetic acid, by performing molecular dynamics and replica exchange molecular dynamics simulations of these nucleosides. Although our simulations using the FF99 force field did not, in general, reproduce the experimentally observed conformational characteristics well, combination of the parameter set with recent revisions of the FF99 force field for RNA showed noticeable improvement for some of the nucleosides.

Unusual base pairing during the decoding of a stop codon by the ribosome

During normal translation, the binding of a release factor to one of the three stop codons (UGA, UAA or UAG) results in the termination of protein synthesis. However, modification of the initial uridine to a pseudouridine (Ψ) allows efficient recognition and read-through of these stop codons by a transfer RNA (tRNA), although it requires the formation of two normally forbidden purine-purine base pairs. Here we determined the crystal structure at 3.1 Å resolution of the 30S ribosomal subunit in complex with the anticodon stem loop of tRNA(Ser) bound to the ΨAG stop codon in the A site. The ΨA base pair at the first position is accompanied by the formation of purine-purine base pairs at the second and third positions of the codon, which show an unusual Watson-Crick/Hoogsteen geometry. The structure shows a previously unsuspected ability of the ribosomal decoding centre to accommodate non-canonical base pairs.

Pseudouridine synthase 1: a site-specific synthase without strict sequence recognition requirements

Pseudouridine synthase 1 (Pus1p) is an unusual site-specific modification enzyme in that it can modify a number of positions in tRNAs and can recognize several other types of RNA. No consensus recognition sequence or structure has been identified for Pus1p. Human Pus1p was used to determine which structural or sequence elements of human tRNA^Ser are necessary for pseudouridine (Ψ) formation at position 28 in the anticodon stem-loop (ASL). Some point mutations in the ASL stem of tRNA^Ser had significant effects on the levels of modification and compensatory mutation, to reform the base pair, restored a wild-type level of Ψ formation. Deletion analysis showed that the tRNA^Ser TΨC stem-loop was a determinant for modification in the ASL. A mini-substrate composed of the ASL and TΨC stem-loop exhibited significant Ψ formation at position 28 and a number of mutants were tested. Substantial base pairing in the ASL stem (3 out of 5 bp) is required, but the sequence of the TΨC loop is not required for modification. When all nucleotides in the ASL stem other than U28 were changed in a single mutant, but base pairing was retained, a near wild-type level of modification was observed.

Complete modification maps for the cytosolic small and large subunit rRNAs of Euglena gracilis: functional and evolutionary implications of contrasting patterns between the two rRNA components

In the protist Euglena gracilis, the cytosolic small subunit (SSU) rRNA is a single, covalently continuous species typical of most eukaryotes; in contrast, the large subunit (LSU) rRNA is naturally fragmented, comprising 14 separate RNA molecules instead of the bipartite (28S+5.8S) eukaryotic LSU rRNA typically seen. We present extensively revised secondary structure models of the E. gracilis SSU and LSU rRNAs and have mapped the positions of all of the modified nucleosides in these rRNAs (88 in SSU rRNA and 262 in LSU rRNA, with only 3 LSU rRNA modifications incompletely characterized). The relative proportions of ribose-methylated nucleosides and pseudouridine (∼60% and ∼35%, respectively) are closely similar in the two rRNAs; however, whereas the Euglena SSU rRNA has about the same absolute number of modifications as its human counterpart, the Euglena LSU rRNA has twice as many modifications as the corresponding human LSU rRNA. The increased levels of rRNA fragmentation and modification in E. gracilis LSU rRNA are correlated with a 3-fold increase in the level of mispairing in helical regions compared to the human LSU rRNA. In contrast, no comparable increase in mispairing is seen in helical regions of the SSU rRNA compared to its homologs in other eukaryotes. In view of the reported effects of both ribose-methylated nucleoside and pseudouridine residues on RNA structure, these correlations lead us to suggest that increased modification in the LSU rRNA may play a role in stabilizing a 'looser' structure promoted by elevated helical mispairing and a high degree of fragmentation.

Chemical modification of siRNA bases to probe and enhance RNA interference

Considerable attention has focused on the use of alternatives to the native ribose and phosphate backbone of small interfering RNAs for therapeutic applications of the RNA interference pathway. In this synopsis, we highlight the less common chemical modifications, namely, those of the RNA nucleobases. Base modifications have the potential to lend insight into the mechanism of gene silencing and to lead to novel methods to overcome off-target effects that arise due to deleterious protein binding or mis-targeting of mRNA.

Mass spectrometry-based quantification of pseudouridine in RNA

Direct detection of pseudouridine (ψ), an isomer of uridine, in RNA is challenging. The most popular method requires chemical derivatization using N-cyclohexyl-N'-β-(4-methylmorpholinum ethyl) carbodiimide p-tosylate (CMCT) followed by radiolabeled primer extension mediated by reverse transcriptase. More recently, mass spectrometry (MS)-based approaches for sequence placement of pseudouridine in RNA have been developed. Nearly all of these approaches, however, only yield qualitative information regarding the presence or absence of pseudouridine in a given RNA population. Here, we have extended a previously developed liquid chromatography tandem mass spectrometry (LC-MS/MS) method to enable both the qualitative and quantitative analysis of pseudouridine. Quantitative selected reaction monitoring (SRM) assays were developed using synthetic oligonucleotides, with or without pseudouridine, and the results yielded a linear relationship between the ion abundance of the pseudouridine-specific fragment ion and the amount of pseudouridine-containing oligonucleotide present in the original sample. Using this quantitative SRM assay, the extent of pseudouridine hypomodification in the conserved T-loop of tRNA isolated from two different Escherichia coli strains was established.

Preparation of short interfering RNA containing the modified nucleosides 2-thiouridine, pseudouridine, or dihydrouridine

Modified uridine derivatives such as 2-thiouridine (s(2)U), pseudouridine (Psi), and dihydrouridine (D) are naturally existing nucleoside units identified in tRNA molecules. Recently, we have shown that such base-modified units introduced into functionally important sites of siRNA modulate thermodynamic stability of the duplex and its gene silencing activity. In this unit, we describe chemical synthesis of 3'-phosphoramidite derivatives of s(2)U and D units (the 3'-phosphoramidite derivative of Psi is commercially available), and their use for the synthesis of RNA oligonucleotides according to the routine phosphoramidite protocol. The only exception concerns the oxidation step with I(2)/pyridine/water which, if applied towards oligonucleotides containing s(2)U units, would lead to the loss of sulfur. Therefore, to avoid this side reaction, tert-butyl hydroperoxide is used as an oxidizing reagent. After the oligonucleotide chain assembly is completed, the resulting oligomer is deprotected under mild basic conditions (MeNH(2)/EtOH/DMSO) to avoid dihydrouracil ring opening, which is a reported side-reaction during the routine synthesis of dihydrouridine-containing RNA. Oligonucleotides modified with s(2)U, D, or Psi units are useful models for structure-function studies. Here, the procedure for preparation of siRNA duplexes is described.

Gain and loss of an intron in a protein-coding gene in Archaea: the case of an archaeal RNA pseudouridine synthase gene

Background

We previously found the first examples of splicing of archaeal pre-mRNAs for homologs of the eukaryotic CBF5 protein (also known as dyskerin in humans) in Aeropyrum pernix, Sulfolobus solfataricus, S. tokodaii, and S. acidocaldarirus, and also showed that crenarchaeal species in orders Desulfurococcales and Sulfolobales, except for Hyperthermus butylicus, Pyrodictium occultum, Pyrolobus fumarii, and Ignicoccus islandicus, contain the (putative) cbf5 intron. However, the exact timing of the intron insertion was not determined and verification of the putative secondary loss of the intron in some lineages was not performed.

Results

In the present study, we determined approximately two-thirds of the entire coding region of crenarchaeal Cbf5 sequences from 43 species. A phylogenetic analysis of our data and information from the available genome sequences suggested that the (putative) cbf5 intron existed in the common ancestor of the orders Desulfurococcales and Sulfolobales and that probably at least two independent lineages in the order Desulfurococcales lost the (putative) intron.

Conclusion

This finding is the first observation of a lineage-specific loss of a pre-mRNA intron in Archaea. As the insertion or deletion of introns in protein-coding genes in Archaea has not yet been seriously considered, our finding suggests the possible difficulty of accurately and completely predicting protein-coding genes in Archaea.

Partial activity is seen with many substitutions of highly conserved active site residues in human Pseudouridine synthase 1

Pseudouridine synthase 1 (Pus1p) is an enzyme that converts uridine to Pseudouridine (Psi) in tRNA and other RNAs in eukaryotes. The active site of Pus1p is composed of stretches of amino acids that are highly conserved and it is hypothesized that mutation of select residues would impair the enzyme's ability to catalyze the formation of Psi. However, most mutagenesis studies have been confined to substitution of the catalytic aspartate, which invariably results in an inactive enzyme in all Psi synthases tested. To determine the requirements for particular amino acids at certain absolutely conserved positions in Pus1p, three residues (R116, Y173, R267) that correspond to amino acids known to compose the active site of TruA, a bacterial Psi synthase that is homologous to Pus1p, were mutated in human Pus1p (hPus1p). The effects of those mutations were determined with three different in vitro assays of pseudouridylation and several tRNA substrates. Surprisingly, it was found that each of these components of the hPus1p active site could tolerate certain amino acid substitutions and in fact most mutants exhibited some activity. The most active mutants retained near wild-type activity at positions 27 or 28 in the substrate tRNA, but activity was greatly reduced or absent at other positions in tRNA readily modified by wild-type hPus1p.