Specificity and nonspecificity in RNA-protein interactions

HnRNP D activates production of HPV16 E1 and E6 mRNAs by promoting intron retention

Human papillomavirus type 16 (HPV16) E1 and E6 proteins are produced from mRNAs with retained introns, but it has been unclear how these mRNAs are generated. Here, we report that hnRNP D act as a splicing inhibitor of HPV16 E1/E2- and E6/E7-mRNAs thereby generating intron-containing E1- and E6-mRNAs, respectively. N- and C-termini of hnRNP D contributed to HPV16 mRNA splicing control differently. HnRNP D interacted with the components of splicing machinery and with HPV16 RNA to exert its inhibitory function. As a result, the cytoplasmic levels of intron-retained HPV16 mRNAs were increased in the presence of hnRNP D. Association of hnRNP D with HPV16 mRNAs in the cytoplasm was observed, and this may correlate with unexpected inhibition of HPV16 E1- and E6-mRNA translation. Notably, hnRNP D40 interacted with HPV16 mRNAs in an HPV16-driven tonsillar cancer cell line and in HPV16-immortalized human keratinocytes. Furthermore, knockdown of hnRNP D in HPV16-driven cervical cancer cells enhanced production of the HPV16 E7 oncoprotein. Our results suggest that hnRNP D plays significant roles in the regulation of HPV gene expression and HPV-associated cancer development.

Non-Darwinian Molecular Biology

With the discovery of the double helical structure of DNA, a shift occurred in how biologists investigated questions surrounding cellular processes, such as protein synthesis. Instead of viewing biological activity through the lens of chemical reactions, this new field used biological information to gain a new profound view of how biological systems work. Molecular biologists asked new types of questions that would have been inconceivable to the older generation of researchers, such as how cellular machineries convert inherited biological information into functional molecules like proteins. This new focus on biological information also gave molecular biologists a way to link their findings to concepts developed by genetics and the modern synthesis. However, by the late 1960s this all changed. Elevated rates of mutation, unsustainable genetic loads, and high levels of variation in populations, challenged Darwinian evolution, a central tenant of the modern synthesis, where adaptation was the main driver of evolutionary change. Building on these findings, Motoo Kimura advanced the neutral theory of molecular evolution, which advocates that selection in multicellular eukaryotes is weak and that most genomic changes are neutral and due to random drift. This was further elaborated by Jack King and Thomas Jukes, in their paper “Non-Darwinian Evolution”, where they pointed out that the observed changes seen in proteins and the types of polymorphisms observed in populations only become understandable when we take into account biochemistry and Kimura’s new theory. Fifty years later, most molecular biologists remain unaware of these fundamental advances. Their adaptionist viewpoint fails to explain data collected from new powerful technologies which can detect exceedingly rare biochemical events. For example, high throughput sequencing routinely detects RNA transcripts being produced from almost the entire genome yet are present less than one copy per thousand cells and appear to lack any function. Molecular biologists must now reincorporate ideas from classical biochemistry and absorb modern concepts from molecular evolution, to craft a new lens through which they can evaluate the functionality of transcriptional units, and make sense of our messy, intricate, and complicated genome.

Challenges for machine learning in RNA-protein interaction prediction

RNA-protein interactions have long being recognised as crucial regulators of gene expression. Recently, the development of scalable experimental techniques to measure these interactions has revolutionised the field, leading to the production of large-scale datasets which offer both opportunities and challenges for machine learning techniques. In this brief note, we will discuss some of the major stumbling blocks towards the use of machine learning in computational RNA biology, focusing specifically on the problem of predicting RNA-protein interactions from next-generation sequencing data.

Y-box Binding Protein 1: Looking Back to the Future

Y-box binding protein 1 is a member of the cold shock domain (CSD) protein family and one of the most studied proteins associated with a large number of human diseases. This review aims to critically reassess the growing number of pathological functions ascribed to YB-1 in the past decades. The focus is given on the important role of YB-1 and related CSD proteins in the physiology of normal cells. The functional significance of these proteins is highlighted by their high evolutionary conservation from bacteria to men, where they are ubiquitously expressed and involved in coordinating all steps of mRNA biogenesis, including transcription, translation, storage, and degradation. Their activities are especially important under conditions requiring rapid change in the gene expression programs, such as early embryonic development, differentiation, stress, and adaptation to new environments. Therefore, to define a precise role of YB-1 in tumorigenic transformation and in other pathological conditions, it is important to understand its basic properties and functions in normal cells, and how they are interrupted in complex diseases including cancer.

Modulation of Phase Separation by RNA: A Glimpse on N6-Methyladenosine Modification

Phase separation is the driving force behind formation of various biomolecular condensates (BioMCs), which sub-compartmentalize certain cellular components in a membraneless manner to orchestrate numerous biological processes. Many BioMCs are composed of proteins and RNAs. While the features and functions of proteins are well studied, less attention was paid to the other essential component RNAs. Here, we describe how RNA contributes to the biogenesis, dissolution, and properties of BioMCs as a multivalence providing scaffold for proteins/RNA to undergo phase separation. Specifically, we focus on N⁶-methyladenosine (m⁶A), the most widely distributed dynamic post-transcriptional modification, which would change the charge, conformation, and RNA-binding protein (RBP) anchoring of modified RNA. m⁶A RNA-modulated phase separation is a new perspective to illustrate m⁶A-mediated various biological processes. We summarize m⁶A main functions as “beacon” to recruit reader proteins and “structural switcher” to alter RNA–protein and RNA–RNA interactions to modulate phase separation and regulate the related biological processes.

RBPSpot: Learning on appropriate contextual information for RBP binding sites discovery

Identifying the factors determining the RBP-RNA interactions remains a big challenge. It involves sparse binding motifs and a suitable sequence context for binding. The present work describes an approach to detect RBP binding sites in RNAs using an ultra-fast inexact k-mers search for statistically significant seeds. The seeds work as an anchor to evaluate the context and binding potential using flanking region information while leveraging from Deep Feed-forward Neural Network. The developed models also received support from MD-simulation studies. The implemented software, RBPSpot, scored consistently high for all the performance metrics including average accuracy of ∼90% across a large number of validated datasets. It outperformed the compared tools, including some with much complex deep-learning models, during a comprehensive benchmarking process. RBPSpot can identify RBP binding sites in the human system and can also be used to develop new models, making it a valuable resource in the area of regulatory system studies.

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Efficient motif anchoring helps to get good quality contextual information on binding

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Realistic and high granularity datasets ensure better performance of the classifiers

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DNN models on the contextual features outperform more complex deep learning tools

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RBPSpot algorithm may be used to develop RBP binding models for other species also

Capture of the newly transcribed RNA interactome using click chemistry

Application of synthetic nucleoside analogues to capture newly transcribed RNAs has unveiled key features of RNA metabolism. Whether this approach could be adapted to isolate the RNA-bound proteome (RNA interactome) was, however, unexplored. We have developed a new method (capture of the newly transcribed RNA interactome using click chemistry, or RICK) for the systematic identification of RNA-binding proteins based on the incorporation of 5-ethynyluridine into newly transcribed RNAs followed by UV cross-linking and click chemistry-mediated biotinylation. The RNA-protein adducts are then isolated by affinity capture using streptavidin-coated beads. Through high-throughput RNA sequencing and mass spectrometry, the RNAs and proteins can be elucidated globally. A typical RICK experimental procedure takes only 1 d, excluding the steps of cell preparation, 5-ethynyluridine labeling, validation (silver staining, western blotting, quantitative reverse-transcription PCR (qRT-PCR) or RNA sequencing (RNA-seq)) and proteomics. Major advantages of RICK are the capture of RNA-binding proteins interacting with any type of RNA and, particularly, the ability to discern between newly transcribed and steady-state RNAs through controlled labeling. Thanks to its versatility, RICK will facilitate the characterization of the total and newly transcribed RNA interactome in different cell types and conditions.

Interactions between long non‑coding RNAs and RNA‑binding proteins in cancer (Review)

Long non-coding RNAs (lncRNAs) fulfill important roles in the majority of cellular processes. Previous studies have demonstrated that lncRNAs are involved in the pathogenesis of various diseases, including cancer. However, to date, the functions of only a small number of the known lncRNAs have been well-documented. lncRNAs comprise a class of multifunctional non-coding transcripts that are able to interact with different types of biomolecules. Interactions between lncRNAs and RNA-binding proteins (RBPs) provide an important mechanism through which lncRNAs exert their regulatory functions, mainly through findings on ‘generalized RBPs’. Regulatory effects on lncRNAs mediated by RBPs have also been explored. Taking account of the research that has been completed to date, the continued and in-depth study of the bidirectional interactions between lncRNAs and RBPs will prove to be of major importance for understanding the pathogenesis of cancer and for developing effective therapies. The present review aims to explore the interactions between lncRNAs and RBPs that have been investigated in cancer, taking into consideration several different aspects, including the regulation of expression, subcellular localization and the mediation of diverse functions.

The regulatory impact of RNA-binding proteins on microRNA targeting

Argonaute is the primary mediator of metazoan miRNA targeting (MT). Among the currently identified >1,500 human RNA-binding proteins (RBPs), there are only a handful of RBPs known to enhance MT and several others reported to suppress MT, leaving the global impact of RBPs on MT elusive. In this study, we have systematically analyzed transcriptome-wide binding sites for 150 human RBPs and evaluated the quantitative effect of individual RBPs on MT efficacy. In contrast to previous studies, we show that most RBPs significantly affect MT and that all of those MT-regulating RBPs function as MT enhancers rather than suppressors, by making the local secondary structure of the target site accessible to Argonaute. Our findings illuminate the unappreciated regulatory impact of human RBPs on MT, and as these RBPs may play key roles in the gene regulatory network governed by metazoan miRNAs, MT should be understood in the context of co-regulating RBPs.

miRNAs are loaded into Argonaute protein and repress complementary mRNA targets. Here the authors show the unappreciated role of RNA binding proteins for efficient miRNA targeting and expand the current understanding of miRNA targeting.

Non-microRNA binding competitively inhibits LIN28 regulation

RNA binding protein (RBP) expression is finite. For RBPs that are vastly outnumbered by their potential target sites, a simple competition for binding can set the magnitude of post-transcriptional control. Here, we show that LIN28, best known for its direct regulation of let-7 miRNA biogenesis, is also indirectly regulated by its widespread binding of non-miRNA transcripts. Approximately 99% of LIN28 binding sites are found on non-miRNA transcripts, like protein coding and ribosomal RNAs. These sites are bound specifically and strongly, but they do not appear to mediate direct post-transcriptional regulation. Instead, non-miRNA sites act to sequester LIN28 protein and effectively change its functional availability, thus impeding the regulation of let-7 in cells. Together, these data show that the binding properties of the transcriptome broadly influence the ability of an RBP to mediate changes in RNA metabolism and gene expression.

Mechanisms and regulation underlying membraneless organelle plasticity control

Evolution has enabled living cells to adopt their structural and functional complexity by organizing intricate cellular compartments, such as membrane-bound and membraneless organelles (MLOs), for spatiotemporal catalysis of physiochemical reactions essential for cell plasticity control. Emerging evidence and view support the notion that MLOs are built by multivalent interactions of biomolecules via phase separation and transition mechanisms. In healthy cells, dynamic chemical modifications regulate MLO plasticity, and reversible phase separation is essential for cell homeostasis. Emerging evidence revealed that aberrant phase separation results in numerous neurodegenerative disorders, cancer, and other diseases. In this review, we provide molecular underpinnings on (i) mechanistic understanding of phase separation, (ii) unifying structural and mechanistic principles that underlie this phenomenon, (iii) various mechanisms that are used by cells for the regulation of phase separation, and (iv) emerging therapeutic and other applications.

[Advances in technologies for large-scale enrichment and identification of ribonucleic acid-protein complexes]

核糖核酸(RNA)在细胞中并非单独存在,从它们产生到被降解的过程中与大量蛋白质发生相互作用,RNA结合蛋白(RNA-binding proteins, RBPs)能与RNA结合形成RNA-蛋白质复合物(RP复合物),并以这种复合物的形式发挥生理功能。RNAs或RBPs任一组分的异常与缺失都会影响RP复合物的正常生理功能,从而导致疾病的发生,如代谢异常、肌肉萎缩症、自身免疫性疾病和癌症。因此,定性定量分析RBPs及其在正常细胞和肿瘤细胞中与RNAs靶标之间的复杂相互作用网络有助于挖掘RP复合物在肿瘤发生发展中的作用,开发肿瘤生物标志物和新的治疗方式。要深入研究和理解RNAs与RBPs的相互作用网络,须依赖组学技术对RP复合物进行大规模鉴定。而作为在组学层面系统性解析RP复合物组成、含量和功能的第一步,大规模富集RP复合物极具挑战性。为了解决这一难题,研究者们发展了各种富集鉴定策略。该文针对RP复合物富集策略的最新进展进行了综述,包括紫外光交联和免疫沉淀(crosslinking and immunoprecipitation, CLIP)及其衍生技术、基于“点击化学”的富集策略和基于相分离的富集策略,比较分析了它们的技术原理、优缺点,以方便研究者们选择合适的策略来解决感兴趣的生物学问题。该文最后总结了当前的RP复合物富集方法仍然存在富集效率低和操作繁琐等亟需解决的技术挑战,为富集策略的发展提供了研究方向。

Reovirus Nonstructural Protein σNS Recruits Viral RNA to Replication Organelles

The function of the mammalian orthoreovirus (reovirus) σNS nonstructural protein is enigmatic. σNS is an RNA-binding protein that forms oligomers and enhances the stability of bound RNAs, but the mechanisms by which it contributes to reovirus replication are unknown. To determine the function of σNS-RNA binding in reovirus replication, we engineered σNS mutants deficient in RNA-binding capacity. We found that alanine substitutions of positively charged residues in a predicted RNA-binding domain decrease RNA-dependent oligomerization. To define steps in reovirus replication facilitated by the RNA-binding property of σNS, we established a complementation system in which wild-type or mutant forms of σNS could be tested for the capacity to overcome inhibition of σNS expression. Mutations in σNS that disrupt RNA binding also diminish viral replication and σNS distribution to viral factories. Moreover, viral mRNAs only incorporate into viral factories or factory-like structures (formed following expression of nonstructural protein μNS) when σNS is present and capable of binding RNA. Collectively, these findings indicate that σNS requires positively charged residues in a putative RNA-binding domain to recruit viral mRNAs to sites of viral replication and establish a function for σNS in reovirus replication.

Norovirus VPg Binds RNA through a Conserved N-Terminal K/R Basic Patch

The viral protein genome-linked (VPg) of noroviruses is a multi-functional protein that participates in essential roles during the viral replication cycle. Predictive analyses indicate that murine norovirus (MNV) VPg contains a disordered N-terminal region with RNA binding potential. VPg proteins were expressed with an N-terminal spidroin fusion protein in insect cells and the interaction with RNA investigated by electrophoretic mobility shift assays (EMSA) against a series of RNA probes (pentaprobes) representing all possible five nucleotide combinations. MNV VPg and human norovirus (HuNV) VPg proteins were directly bound to RNA in a non-specific manner. To identify amino acids involved in binding to RNA, all basic (K/R) residues in the first 12 amino acids of MNV VPg were mutated to alanine. Removal of the K/R amino acids eliminated RNA binding and is consistent with a K/R basic patch RNA binding motif within the disordered N-terminal region of norovirus VPgs. Finally, we show that mutation of the K/R basic patch required for RNA binding eliminates the ability of MNV VPg to induce a G0/G1 cell cycle arrest.

StoatyDive: Evaluation and classification of peak profiles for sequencing data

BACKGROUND

The prediction of binding sites (peak-calling) is a common task in the data analysis of methods such as cross-linking immunoprecipitation in combination with high-throughput sequencing (CLIP-Seq). The predicted binding sites are often further analyzed to predict sequence motifs or structure patterns. When looking at a typical result of such high-throughput experiments, the obtained peak profiles differ largely on a genomic level. Thus, a tool is missing that evaluates and classifies the predicted peaks on the basis of their shapes. We hereby present StoatyDive, a tool that can be used to filter for specific peak profile shapes of sequencing data such as CLIP.

FINDINGS

With StoatyDive we are able to classify peak profile shapes from CLIP-seq data of the histone stem-loop-binding protein (SLBP). We compare the results to existing tools and show that StoatyDive finds more distinct peak shape clusters for CLIP data. Furthermore, we present StoatyDive's capabilities as a quality control tool and as a filter to pick different shapes based on biological or technical questions for other CLIP data from different RNA binding proteins with different biological functions and numbers of RNA recognition motifs. We finally show that proteins involved in splicing, such as RBM22 and U2AF1, have potentially sharper-shaped peaks than other RNA binding proteins.

CONCLUSION

StoatyDive finally fills the demand for a peak shape clustering tool for CLIP-Seq data that fine-tunes downstream analysis steps such as structure or sequence motif predictions and that acts as a quality control.

Nuclear scaffold protein p54nrb/NONO facilitates the hypoxia-enhanced progression of hepatocellular carcinoma

Hypoxia and related oxidative stress are closely related to the development and treatment of hepatocellular carcinoma (HCC). However, the mechanism mediated by hypoxia in HCC has not yet been elucidated. Here, we found multifunction scaffold protein p54^nrb/NONO exerted pleiotropic effects to regulate hypoxia transcription signals, thereby enhancing the progression of liver cancer. Extensive analysis of clinical data demonstrated that NONO was significantly upregulated and represented as a poor prognostic indicator of HCC. The crucial role of NONO in driving angiogenesis and glycolysis, two well-known cancer phenotypes mediated by hypoxia, was examined in vitro an in vivo. Mechanistically, NONO interacted with and stabilized both HIF-1 and HIF-2 complexes thus activating the transcription of hypoxia-induced genes. Besides, NONO bound pre-mRNA and subsequent mRNA of these genes to facilitate them splicing and mRNA stability, respectively. Thus, NONO knockout seriously disrupted the expression of a cluster of HIF-1/2 targets and impeded hypoxia-enhanced progression in HCC. In conclusion, NONO functioned as a multipurpose scaffold that interacted with HIF-1/2 complex and their downstream transcripts to facilitate the expression of hypoxia-induced genes, allowing malignant proliferation, indicating that NONO might be a potential therapeutic target for HCC.

Zooming in on protein-RNA interactions: a multi-level workflow to identify interaction partners

Interactions between proteins and RNA are at the base of numerous cellular regulatory and functional phenomena. The investigation of the biological relevance of non-coding RNAs has led to the identification of numerous novel RNA-binding proteins (RBPs). However, defining the RNA sequences and structures that are selectively recognised by an RBP remains challenging, since these interactions can be transient and highly dynamic, and may be mediated by unstructured regions in the protein, as in the case of many non-canonical RBPs. Numerous experimental and computational methodologies have been developed to predict, identify and verify the binding between a given RBP and potential RNA partners, but navigating across the vast ocean of data can be frustrating and misleading. In this mini-review, we propose a workflow for the identification of the RNA binding partners of putative, newly identified RBPs. The large pool of potential binders selected by in-cell experiments can be enriched by in silico tools such as catRAPID, which is able to predict the RNA sequences more likely to interact with specific RBP regions with high accuracy. The RNA candidates with the highest potential can then be analysed in vitro to determine the binding strength and to precisely identify the binding sites. The results thus obtained can furthermore validate the computational predictions, offering an all-round solution to the issue of finding the most likely RNA binding partners for a newly identified potential RBP.

Structures and target RNA preferences of the RNA-binding protein family of IGF2BPs: An overview

Insulin-like growth factor 2 mRNA-binding proteins (IMPs, IGF2BPs) act in mRNA transport and translational control but are oncofetal tumor marker proteins. The IMP protein family represents a number of bona fide multi-domain RNA-binding proteins with up to six RNA-binding domains, resulting in a high complexity of possible modes of interactions with target mRNAs. Their exact mechanism in stability control of oncogenic mRNAs is only partially understood. Our and other laboratories' recent work has significantly pushed the understanding of IMP protein specificities both toward RNA engagement and between each other from NMR and crystal structures serving the basis for systematic biochemical and functional investigations. We here summarize the known structural and biochemical information about IMP RNA-binding domains and their RNA preferences. The article also touches on the respective roles of RNA secondary and protein tertiary structures for specific RNA-protein complexes, including the limited knowledge about IMPs' protein-protein interactions, which are often RNA mediated.

A new tandem enrichment strategy for the simultaneous profiling of O-GlcNAcylation and phosphorylation in RNA-binding proteome

RNA-protein interactions play important roles in almost every step of the lifetime of RNAs, such as RNA splicing, transporting, localization, translation and degradation. Post-translational modifications, such as O-GlcNAcylation and phosphorylation, and their "cross-talk" (OPCT) are essential to the activity and function regulation of RNA-binding proteins (RBPs). However, due to the extremely low abundance of O-GlcNAcylation and the lack of RBP-targeted enrichment strategies, large-scale simultaneous profiling of O-GlcNAcylation and phosphorylation on RBPs is still a challenging task. In the present study, we developed a tandem enrichment strategy combining metabolic labeling-based RNA tagging for selective purification of RBPs and HILIC-based enrichment for simultaneous O-GlcNAcylation and phosphorylation profiling. Benefiting from the sequence-independent RNA tagging by ethynyluridine (EU) labeling, 1115 RBPs binding to different types of RNAs were successfully enriched and identified by quantitative mass spectrometry (MS) analysis. Further HILIC enrichment on the tryptic-digested RBPs and MS analysis led to the first large-scale identification of O-GlcNAcylation and phosphorylation in the RNA-binding proteome, with 461 O-GlcNAc peptides corresponding to 300 RBPs and 671 phosphopeptides corresponding to 389 RBPs. Interestingly, ∼25% RBPs modified by two PTMs were found to be related to multiple metabolism pathways. This strategy has the advantage of high compatibility with MS and provides peptide-level evidence for the identification of O-GlcNAcylated RBPs. We expect it will support simultaneous mapping of O-GlcNAcylation and phosphorylation on RBPs and facilitate further elucidation of the crucial roles of OPCT in the function regulation of RBPs.

Protein-DNA/RNA Interactions: An Overview of Investigation Methods in the -Omics Era

The fields of application of functional proteomics are not limited to the study of protein–protein interactions; they also extend to those involving protein complexes that bind DNA or RNA. These interactions affect fundamental processes such as replication, transcription, and repair in the case of DNA, as well as transport, translation, splicing, and silencing in the case of RNA. Analytical or preparative experimental approaches, both in vivo and in vitro, have been developed to isolate and identify DNA/RNA binding proteins by exploiting the advantage of the affinity shown by these proteins toward a specific oligonucleotide sequence. The present review proposes an overview of the approaches most commonly employed in proteomics applications for the identification of nucleic acid-binding proteins, such as affinity purification (AP) protocols, EMSA, chromatin purification methods, and CRISPR-based chromatin affinity purification, which are generally associated with mass spectrometry methodologies for the unbiased protein identification.

HIV detection from human serum with paper-based isotachophoretic RNA extraction and reverse transcription recombinase polymerase amplification

The number of people living with HIV continues to increase with the current total near 38 million, of which about 26 million are receiving antiretroviral therapy (ART). These treatment regimens are highly effective when properly managed, requiring routine viral load monitoring to assess successful viral suppression. Efforts to expand access by decentralizing HIV nucleic acid testing in low- and middle-income countries (LMICs) has been hampered by the cost and complexity of current tests. Sample preparation of blood samples has traditionally relied on cumbersome RNA extraction methods, and it continues to be a key bottleneck for developing low-cost POC nucleic acid tests. We present a microfluidic paper-based analytical device (μPAD) for extracting RNA and detecting HIV in serum, leveraging low-cost materials, simple buffers, and an electric field. We detect HIV virions and MS2 bacteriophage internal control in human serum using a novel lysis and RNase inactivation method, paper-based isotachophoresis (ITP) for RNA extraction, and duplexed reverse transcription recombinase polymerase amplification (RT-RPA) for nucleic acid amplification. We design a specialized ITP system to extract and concentrate RNA, while excluding harsh reagents used for lysis and RNase inactivation. We found the ITP μPAD can extract and purify 5000 HIV RNA copies per mL of serum. We then demonstrate detection of HIV virions and MS2 bacteriophage in human serum within 45-minutes.

Predicting dynamic cellular protein-RNA interactions by deep learning using in vivo RNA structures

Interactions with RNA-binding proteins (RBPs) are integral to RNA function and cellular regulation, and dynamically reflect specific cellular conditions. However, presently available tools for predicting RBP-RNA interactions employ RNA sequence and/or predicted RNA structures, and therefore do not capture their condition-dependent nature. Here, after profiling transcriptome-wide in vivo RNA secondary structures in seven cell types, we developed PrismNet, a deep learning tool that integrates experimental in vivo RNA structure data and RBP binding data for matched cells to accurately predict dynamic RBP binding in various cellular conditions. PrismNet results for 168 RBPs support its utility for both understanding CLIP-seq results and largely extending such interaction data to accurately analyze additional cell types. Further, PrismNet employs an "attention" strategy to computationally identify exact RBP-binding nucleotides, and we discovered enrichment among dynamic RBP-binding sites for structure-changing variants (riboSNitches), which can link genetic diseases with dysregulated RBP bindings. Our rich profiling data and deep learning-based prediction tool provide access to a previously inaccessible layer of cell-type-specific RBP-RNA interactions, with clear utility for understanding and treating human diseases.

Parallel genetics of regulatory sequences using scalable genome editing in vivo

How regulatory sequences control gene expression is fundamental for explaining phenotypes in health and disease. Regulatory elements must ultimately be understood within their genomic environment and development- or tissue-specific contexts. Because this is technically challenging, few regulatory elements have been characterized in vivo. Here, we use inducible Cas9 and multiplexed guide RNAs to create hundreds of mutations in enhancers/promoters and 3' UTRs of 16 genes in C. elegans. Our software crispr-DART analyzes indel mutations in targeted DNA sequencing. We quantify the impact of mutations on expression and fitness by targeted RNA sequencing and DNA sampling. When applying our approach to the lin-41 3' UTR, generating hundreds of mutants, we find that the two adjacent binding sites for the miRNA let-7 can regulate lin-41 expression independently of each other. Finally, we map regulatory genotypes to phenotypic traits for several genes. Our approach enables parallel analysis of regulatory sequences directly in animals.

The World of Stable Ribonucleoproteins and Its Mapping With Grad-Seq and Related Approaches

Macromolecular complexes of proteins and RNAs are essential building blocks of cells. These stable supramolecular particles can be viewed as minimal biochemical units whose structural organization, i.e., the way the RNA and the protein interact with each other, is directly linked to their biological function. Whether those are dynamic regulatory ribonucleoproteins (RNPs) or integrated molecular machines involved in gene expression, the comprehensive knowledge of these units is critical to our understanding of key molecular mechanisms and cell physiology phenomena. Such is the goal of diverse complexomic approaches and in particular of the recently developed gradient profiling by sequencing (Grad-seq). By separating cellular protein and RNA complexes on a density gradient and quantifying their distributions genome-wide by mass spectrometry and deep sequencing, Grad-seq charts global landscapes of native macromolecular assemblies. In this review, we propose a function-based ontology of stable RNPs and discuss how Grad-seq and related approaches transformed our perspective of bacterial and eukaryotic ribonucleoproteins by guiding the discovery of new RNA-binding proteins and unusual classes of noncoding RNAs. We highlight some methodological aspects and developments that permit to further boost the power of this technique and to look for exciting new biology in understudied and challenging biological models.

Tandem RNA binding sites induce self-association of the stress granule marker protein TIA-1

TIA-1 is an RNA-binding protein that sequesters target RNA into stress granules under conditions of cellular stress. Promotion of stress granule formation by TIA-1 depends upon self-association of its prion-like domain that facilitates liquid-liquid phase separation and is thought to be enhanced via RNA binding. However, the mechanisms underlying the influence of RNA on TIA-1 self-association have not been previously demonstrated. Here we have investigated the self-associating properties of full-length TIA-1 in the presence of designed and native TIA-1 nucleic acid binding sites in vitro, monitoring phase separation, fibril formation and shape. We show that single stranded RNA and DNA induce liquid-liquid phase separation of TIA-1 in a multisite, sequence-specific manner and also efficiently promote formation of amyloid-like fibrils. Although RNA binding to a single site induces a small conformational change in TIA-1, this alone does not enhance phase separation of TIA-1. Tandem binding sites are required to enhance phase separation of TIA-1 and this is finely tuned by the protein:binding site stoichiometry rather than nucleic acid length. Native tandem TIA-1 binding sites within the 3′ UTR of p53 mRNA also efficiently enhance phase separation of TIA-1 and thus may potentially act as potent nucleation sites for stress granule assembly.

CircRNA-Protein Interactions in Muscle Development and Diseases

Circular RNA (circRNA) is a kind of novel endogenous noncoding RNA formed through back-splicing of mRNA precursor. The biogenesis, degradation, nucleus-cytoplasm transport, location, and even translation of circRNA are controlled by RNA-binding proteins (RBPs). Therefore, circRNAs and the chaperoned RBPs play critical roles in biological functions that significantly contribute to normal animal development and disease. In this review, we systematically characterize the possible molecular mechanism of circRNA-protein interactions, summarize the latest research on circRNA-protein interactions in muscle development and myocardial disease, and discuss the future application of circRNA in treating muscle diseases. Finally, we provide several valid prediction methods and experimental verification approaches. Our review reveals the significance of circRNAs and their protein chaperones and provides a reference for further study in this field.

Multidimensional crosstalk between RNA-binding proteins and noncoding RNAs in cancer biology

RNA-binding proteins (RBPs) are well-known to bind RNA via a set of RNA-binding domains (RBDs) and determine the fate and function of their RNA targets; inversely, some RBPs, in certain cases, may be modulated by the bound RNAs rather than regulate their RNA partners. Current proteome-wide studies reveal that almost half of RBPs have no canonical RBDs, and the discovery of tens of thousands of noncoding RNAs (ncRNAs), especially those with the size larger than 200 nt (namely long noncoding RNAs, lncRNAs), makes the crosstalk between RBPs and RNAs more complicated. It is clear that macromolecular complexes formed by RBP and RNA are not only a form of existence of their RBP and RNA components in cells, but also represent a functional entity through which those RBPs and regulatory ncRNAs participate in the construction of regulatory networks in organism. In this review, we summarize the multidimensional crosstalk between RBPs and ncRNAs in cancer and discuss how RBPs achieve their function via the bound ncRNAs in different aspects of gene expression as well as how RBPs direct modification and processing of ncRNAs, in order to better understand tumor biology and provide new insights into development of strategies for cancer therapy and early detection.

Identification of Intrinsic RNA Binding Specificity of Purified Proteins by in vitro RNA Immunoprecipitation (vitRIP)

RNA-protein interactions are often mediated by dedicated canonical RNA binding domains. However, interactions through non-canonical domains with unknown specificity are increasingly observed, raising the question how RNA targets are recognized. Knowledge of the intrinsic RNA binding specificity contributes to the understanding of target selectivity and function of an individual protein. The presented in vitro RNA immunoprecipitation assay (vitRIP) uncovers intrinsic RNA binding specificities of isolated proteins using the total cellular RNA pool as a library. Total RNA extracted from cells or tissues is incubated with purified recombinant proteins, RNA-protein complexes are immunoprecipitated and bound transcripts are identified by deep sequencing or quantitative RT-PCR. Enriched RNA classes and the nucleotide frequency in these RNAs inform on the intrinsic specificity of the recombinant protein. The simple and versatile protocol can be adapted to other RNA binding proteins and total RNA libraries from any cell type or tissue. Graphic abstract: Figure 1. Schematic of the in vitro RNA immunoprecipitation (vitRIP) protocol.

Crucial roles of different RNA-binding hnRNP proteins in Stem Cells

The self-renewal, pluripotency and differentiation of stem cells are regulated by various genetic and epigenetic factors. As a kind of RNA binding protein (RBP), the heterogeneous nuclear ribonucleoproteins (hnRNPs) can act as "RNA scaffold" and recruit mRNA, lncRNA, microRNA and circRNA to affect mRNA splicing and processing, regulate gene transcription and post-transcriptional translation, change genome structure, and ultimately play crucial roles in the biological processes of cells. Recent researches have demonstrated that hnRNPs are irreplaceable for self-renewal and differentiation of stem cells. hnRNPs function in stem cells by multiple mechanisms, which include regulating mRNA stability, inducing alternative splicing of mRNA, epigenetically regulate gene expression, and maintaining telomerase activity and telomere length. The functions and the underlying mechanisms of hnRNPs in stem cells deserve further investigation.

RNA-PROTACs: Degraders of RNA-Binding Proteins

Defects in the functions of RNA binding proteins (RBPs) are at the origin of many diseases; however, targeting RBPs with conventional drugs has proven difficult. PROTACs are a new class of drugs that mediate selective degradation of a target protein through a cell's ubiquitination machinery. PROTACs comprise a moiety that binds the selected protein, conjugated to a ligand of an E3 ligase. Herein, we introduce RNA-PROTACs as a new concept in the targeting of RBPs. These chimeric structures employ small RNA mimics as targeting groups that dock the RNA-binding site of the RBP, whereupon a conjugated E3-recruiting peptide derived from the HIF-1α protein directs the RBP for proteasomal degradation. We performed a proof-of-concept demonstration with the degradation of two RBPs-a stem cell factor LIN28 and a splicing factor RBFOX1-and showed their use in cancer cell lines. The RNA-PROTAC approach opens the way to rapid, selective targeting of RBPs in a rational and general fashion.

A live-cell assay for the detection of pre-microRNA-protein interactions

Recent efforts in genome-wide sequencing and proteomics have revealed the fundamental roles that RNA-binding proteins (RBPs) play in the life cycle and function of coding and non-coding RNAs. While these methodologies provide a systems-level view of the networking of RNA and proteins, approaches to enable the cellular validation of discovered interactions are lacking. Leveraging the power of bioorthogonal chemistry- and split-luciferase-based assay technologies, we have devised a conceptually new assay for the live-cell detection of RNA-protein interactions (RPIs), RNA interaction with Protein-mediated Complementation Assay, or RiPCA. As proof-of-concept, we utilized the interaction of the pre-microRNA, pre-let-7, with its binding partner, Lin28. Using this system, we have demonstrated the selective detection of the pre-let-7-Lin28 RPI in both the cytoplasm and nucleus. Furthermore, we determined that this technology can be used to discern relative affinities for specific sequences as well as of individual RNA binding domains. Thus, RiPCA has the potential to serve as a useful tool in supporting the investigation of cellular RPIs.

The circular RNA circZFR phosphorylates Rb promoting cervical cancer progression by regulating the SSBP1/CDK2/cyclin E1 complex

Background

As a novel type of non-coding RNA, circular RNAs (circRNAs) play a critical role in the initiation and development of various diseases, including cancer. However, the exact function of circRNAs in human cervical cancer remains largely unknown.

Methods

We identified the circRNA signature of upregulated circRNAs between cervical cancer and paired adjacent normal tissues. Using two different cohorts and GEO database, a total of six upregulated circRNAs were identified with a fold change > 2, and P < 0.05. Among these six circRNAs, hsa_circ_0072088 (circZFR) was the only exonic circRNA significantly overexpressed in cervical cancer. Functional experiments were performed to investigate the biological function of circZFR. CircRNA pull-down, circRNA immunoprecipitation (circRIP) and Co-immunoprecipitation (Co-IP) assays were executed to investigate the molecular mechanism underlying the function of circZFR.

Results

Functionally, circZFR knockdown represses the proliferation, invasion, and tumor growth. Furthermore, circRNA pull-down experiments combined with mass spectrometry unveil the interactions of circZFR with Single-Stranded DNA Binding Protein 1 (SSBP1). Mechanistically, circZFR bound with SSBP1, thereby promoting the assembly of CDK2/cyclin E1 complexes. The activation of CDK2/cyclin E1 complexes induced p-Rb phosphorylation, thus releasing activated E2F1 leading to cell cycle progression and cell proliferation.

Conclusion

Our findings provide the first evidence that circZFR is a novel onco-circRNA and might be a potential biomarker and therapeutic target for cervical cancer patients.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13046-021-01849-2.

The many ways Epstein-Barr virus takes advantage of the RNA tool kit

Epstein-Barr virus (EBV) was the first human cancer-causing virus to be discovered over fifty years ago. Given its relatively large genome size for a virus and hence the capacity to store more than mere protein-coding information, EBV also harbours genetic material for producing an array of distinct noncoding (nc)RNAs. The double-stranded nature of its DNA genome allows the utilization of the whole gamut of ncRNA types, including both RNA polymerase II and III transcripts, in devising a sophisticated strategy to ensure its replication upon infection in host cells and evasion of host immune responses. Owing to the development of sensitive technologies in recent years, mostly entailing next-generation sequencing, the list of ncRNA types generated by EBV has expanded now to include two RNAs (EBER1 and EBER2) best categorized as long ncRNAs, dozens of microRNAs, one small nucleolar RNA, stable intronic sequence RNAs, and the most recently discovered circular RNAs. With the application of cutting-edge technology, the molecular mechanisms of some of these noncoding transcripts are beginning to emerge, while others remain yet to be elucidated. As viruses often take advantage of existing molecular pathways established by the host, it is likely that further novel concepts of the greatly unexplored noncoding world can be learned from studying the many EBV ncRNAs.

Possible role played by the SINE2 element in gene regulation, as demonstrated by differential processing and polyadenylation in avirulent strains of E. histolytica

Entamoeba histolytica represents a useful model in parasitic organisms due to its complex genomic organization and survival mechanisms. To counteract pathogenic organisms, it is necessary to characterize their molecular biology to design new strategies to combat them. In this report, we investigated a less-known genetic element, short interspersed nuclear element 2 (SINE2), that is present in this ameba and is highly transcribed and polyadenylated. In this study, we show that in two different nonvirulent strains of E. histolytica, SINE2 is differentially processed into two transcript fragments, that is, a full-length 560-nt fragment and a shorter 393-nt fragment bearing an approximately 18-nt polyadenylation tail. Sequence analysis of the SINE2 transcript showed that a Musashi-like protein may bind to it. Also, two putative Musashi-like sequences were identified on the transcript. Semiquantitative expression analysis of the two Musashi-like proteins identified in the E. histolytica genome (XP_648918 and XP_649094) showed that XP_64094 is overexpressed in the nonvirulent strains tested. The information available in the literature and the results presented in this report indicate that SINE2 may affect other genes, as observed with the epigenetic silencing of the G3 strain, by an antisense mechanism or via RNA-protein interactions that may ultimately be involved in the phenotype of nonvirulent strains of E. histolytica.

Different recognition modes of G-quadruplex RNA between two ALS/FTLD-linked proteins TDP-43 and FUS

Amyotrophic lateral sclerosis/frontotemporal lobar degeneration-linked proteins, TDP-43 and fused in sarcoma (FUS), bind to G-quadruplex-containing mRNAs and transport them to distal neurites for local translation. The specificity and mechanism of G4-RNA binding, however, remain largely unsolved. Using purified full-length TDP-43 and FUS and a set of seven G4-DNA/RNA, we compared their recognition properties of G4-RNAs. Both TDP-43 and FUS recognized and bound to G4-DNA/RNAs, but the target selectivity differed between two proteins. TDP-43 recognized only parallel-stranded G4-DNA/RNAs, leading to stabilize the G4 conformation. In contrast, FUS bound to all three types, parallel, hybrid, and antiparallel, of G4-DNA/RNAs, resulting in deformation of the G4 structure. We then concluded that the target selectivity and the influence on G4 RNA structure differed between TDP-43 and FUS.

Galaxy CLIP-Explorer: a web server for CLIP-Seq data analysis

BACKGROUND

Post-transcriptional regulation via RNA-binding proteins plays a fundamental role in every organism, but the regulatory mechanisms lack important understanding. Nevertheless, they can be elucidated by cross-linking immunoprecipitation in combination with high-throughput sequencing (CLIP-Seq). CLIP-Seq answers questions about the functional role of an RNA-binding protein and its targets by determining binding sites on a nucleotide level and associated sequence and structural binding patterns. In recent years the amount of CLIP-Seq data skyrocketed, urging the need for an automatic data analysis that can deal with different experimental set-ups. However, noncanonical data, new protocols, and a huge variety of tools, especially for peak calling, made it difficult to define a standard.

FINDINGS

CLIP-Explorer is a flexible and reproducible data analysis pipeline for iCLIP data that supports for the first time eCLIP, FLASH, and uvCLAP data. Individual steps like peak calling can be changed to adapt to different experimental settings. We validate CLIP-Explorer on eCLIP data, finding similar or nearly identical motifs for various proteins in comparison with other databases. In addition, we detect new sequence motifs for PTBP1 and U2AF2. Finally, we optimize the peak calling with 3 different peak callers on RBFOX2 data, discuss the difficulty of the peak-calling step, and give advice for different experimental set-ups.

CONCLUSION

CLIP-Explorer finally fills the demand for a flexible CLIP-Seq data analysis pipeline that is applicable to the up-to-date CLIP protocols. The article further shows the limitations of current peak-calling algorithms and the importance of a robust peak detection.

Unexpected specificity within dynamic transcriptional protein-protein complexes

A key functional event in eukaryotic gene activation is the formation of dynamic protein-protein interaction networks between transcriptional activators and transcriptional coactivators. Seemingly incongruent with the tight regulation of transcription, many biochemical and biophysical studies suggest that activators use nonspecific hydrophobic and/or electrostatic interactions to bind to coactivators, with few if any specific contacts. Here a mechanistic dissection of a set of representative dynamic activator•coactivator complexes, comprised of the ETV/PEA3 family of activators and the coactivator Med25, reveals a different molecular recognition model. The data demonstrate that small sequence variations within an activator family significantly redistribute the conformational ensemble of the complex while not affecting overall affinity, and distal residues within the activator-not often considered as contributing to binding-play a key role in mediating conformational redistribution. The ETV/PEA3•Med25 ensembles are directed by specific contacts between the disordered activator and the Med25 interface, which is facilitated by structural shifts of the coactivator binding surface. Taken together, these data highlight the critical role coactivator plasticity plays in recognition of disordered activators and indicate that molecular recognition models of disordered proteins must consider the ability of the binding partners to mediate specificity.

Two-step mechanism for selective incorporation of lncRNA into a chromatin modifier

The MLE DExH helicase and the roX lncRNAs are essential components of the chromatin modifying Dosage Compensation Complex (DCC) in Drosophila. To explore the mechanism of ribonucleoprotein complex assembly, we developed vitRIP, an unbiased, transcriptome-wide in vitro assay that reveals RNA binding specificity. We found that MLE has intrinsic specificity for U-/A-rich sequences and tandem stem-loop structures and binds many RNAs beyond roX in vitro. The selectivity of the helicase for physiological substrates is further enhanced by the core DCC. Unwinding of roX2 by MLE induces a highly selective RNA binding surface in the unstructured C-terminus of the MSL2 subunit and triggers-specific association of MLE and roX2 with the core DCC. The exquisite selectivity of roX2 incorporation into the DCC thus originates from intimate cooperation between the helicase and the core DCC involving two distinct RNA selection principles and their mutual refinement.

On the Way to Understanding the Interplay between the RNA Structure and Functions in Cells: A Genome-Wide Perspective

RNAs adopt specific structures in order to perform their biological activities. The structure of RNA is an important layer of gene expression regulation, and can impact a plethora of cellular processes, starting with transcription, RNA processing, and translation, and ending with RNA turnover. The development of high-throughput technologies has enabled a deeper insight into the sophisticated interplay between the structure of the cellular transcriptome and the living cells environment. In this review, we present the current view on the RNA structure in vivo resulting from the most recent transcriptome-wide studies in different organisms, including mammalians, yeast, plants, and bacteria. We focus on the relationship between the mRNA structure and translation, mRNA stability and degradation, protein binding, and RNA posttranscriptional modifications.

Concentration-dependent splicing is enabled by Rbfox motifs of intermediate affinity

The Rbfox family of splicing factors regulate alternative splicing during animal development and in disease, impacting thousands of exons in the maturing brain, heart, and muscle. Rbfox proteins have long been known to bind to the RNA sequence GCAUG with high affinity, but just half of Rbfox binding sites contain a GCAUG motif in vivo. We incubated recombinant RBFOX2 with over 60,000 mouse and human transcriptomic sequences to reveal substantial binding to several moderate-affinity, non-GCAYG sites at a physiologically relevant range of RBFOX concentrations. We find that many of these “secondary motifs” bind Rbfox robustly in cells and that several together can exert regulation comparable to GCAUG in a trichromatic splicing reporter assay. Furthermore, secondary motifs regulate RNA splicing in neuronal development and in neuronal subtypes where cellular Rbfox concentrations are highest, enabling a second wave of splicing changes as Rbfox levels increase.

Non-coding RNAs, metabolic stress and adaptive mechanisms in cancer

Metabolic reprogramming in cancer describes the multifaceted alterations in metabolism that contribute to tumorigenesis. Major determinants of metabolic phenotypes are the changes in signalling pathways associated with oncogenic activation together with cues from the tumor microenvironment. Therein, depleted oxygen and nutrient levels elicit metabolic stress, requiring cancer cells to engage adaptive mechanisms. Non-coding RNAs (ncRNAs) act as regulatory elements within metabolic pathways and their widespread dysregulation in cancer contributes to altered metabolic phenotypes. Indeed, ncRNAs are the regulatory accomplices of many prominent effectors of metabolic reprogramming including c-MYC and HIFs that are activated by metabolic stress. By example, this review illustrates the range of ncRNAs mechanisms impacting these effectors throughout their DNA-RNA-protein lifecycle along with presenting the mechanistic roles of ncRNAs in adaptive responses to glucose, glutamine and lipid deprivation. We also discuss the facultative activation of metabolic enzymes by ncRNAs, a phenomenon which may reflect a broad but currently invisible level of metabolic regulation. Finally, the translational challenges associated with ncRNA discoveries are discussed, emphasizing the gaps in knowledge together with importance of understanding the molecular basis of ncRNA regulatory mechanisms.

Inhibition of RNA-binding proteins with small molecules

Protein-RNA interactions have crucial roles in various cellular activities, which, when dysregulated, can lead to a range of human diseases. The identification of small molecules that target the interaction between RNA-binding proteins (RBPs) and RNA is progressing rapidly and represents a novel strategy for the discovery of chemical probes that facilitate understanding of the cellular functions of RBPs and of therapeutic agents with new mechanisms of action. In this Review, I present a current overview of targeting emerging RBPs using small-molecule inhibitors and recent progress in this burgeoning field. Small-molecule inhibitors that were reported for three representative emerging classes of RBPs, the microRNA-binding protein LIN28, the single-stranded or double-stranded RNA-binding Toll-like receptors and the CRISPR-associated (Cas) proteins, are highlighted from a medicinal-chemistry and chemical-biology perspective. However, although this field is burgeoning, challenges remain in the discovery and characterization of small-molecule inhibitors of RBPs.

mRNA structural dynamics shape Argonaute-target interactions

Small interfering RNAs (siRNAs) promote RNA degradation in a variety of processes and have important clinical applications. siRNAs direct cleavage of target RNAs by guiding Argonaute2 (AGO2) to its target site. Target site accessibility is critical for AGO2-target interactions, but how target site accessibility is controlled in vivo is poorly understood. Here, we use live-cell single-molecule imaging in human cells to determine rate constants of the AGO2 cleavage cycle in vivo. We find that the rate-limiting step in mRNA cleavage frequently involves unmasking of target sites by translating ribosomes. Target site masking is caused by heterogeneous intramolecular RNA-RNA interactions, which can conceal target sites for many minutes in the absence of translation. Our results uncover how dynamic changes in mRNA structure shape AGO2-target recognition, provide estimates of mRNA folding and unfolding rates in vivo, and provide experimental evidence for the role of mRNA structural dynamics in control of mRNA-protein interactions.

RNA-binding proteins in tumor progression

RNA-binding protein (RBP) has a highly dynamic spatiotemporal regulation process and important biological functions. They are critical to maintain the transcriptome through post-transcriptionally controlling the processing and transportation of RNA, including regulating RNA splicing, polyadenylation, mRNA stability, mRNA localization, and translation. Alteration of each process will affect the RNA life cycle, produce abnormal protein phenotypes, and thus lead to the occurrence and development of tumors. Here, we summarize RBPs involved in tumor progression and the underlying molecular mechanisms whereby they are regulated and exert their effects. This analysis is an important step towards the comprehensive characterization of post-transcriptional gene regulation involved in tumor progression.

High throughput approaches to study RNA-protein interactions in vitro

To understand the regulation of gene expression it is critical to determine how proteins interact with and discriminate between different RNAs. In this review, we discuss experimental techniques that utilize high throughput approaches to characterize the interactions of proteins with large numbers of RNAs in vitro. We describe the underlying principles for the main methods, briefly discuss their scope and limitations, and outline how insight from the techniques contributes to our understanding of specificity for RNA-protein interactions.

Enzymatic and Chemical-Based Methods to Inactivate Endogenous Blood Ribonucleases for Nucleic Acid Diagnostics

There are ongoing research efforts into simple and low-cost point-of-care nucleic acid amplification tests (NATs) addressing widespread diagnostic needs in resource-limited clinical settings. Nucleic acid testing for RNA targets in blood specimens typically requires sample preparation that inactivates robust blood ribonucleases (RNases) that can rapidly degrade exogenous RNA. Most NATs rely on decades-old methods that lyse pathogens and inactivate RNases with high concentrations of guanidinium salts. Herein, we investigate alternatives to standard guanidinium-based methods for RNase inactivation using an activity assay with an RNA substrate that fluoresces when cleaved. The effects of proteinase K, nonionic surfactants, SDS, dithiothreitol, and other additives on RNase activity in human serum are reported. Although proteinase K has been widely used in protocols for nuclease inactivation, it was found that high concentrations of proteinase K are unable to eliminate RNase activity in serum, unless used in concert with denaturing concentrations of SDS. It was observed that SDS must be combined with proteinase K, dithiothreitol, or both for irreversible and complete RNase inactivation in serum. This work provides an alternative chemistry for inactivating endogenous RNases for use in simple, low-cost point-of-care NATs for blood-borne pathogens.

Emerging RNA-binding roles in the TRIM family of ubiquitin ligases

TRIM proteins constitute a large, diverse and ancient protein family which play a key role in processes including cellular differentiation, autophagy, apoptosis, DNA repair, and tumour suppression. Mostly known and studied through the lens of their ubiquitination activity as E3 ligases, it has recently emerged that many of these proteins are involved in direct RNA binding through their NHL or PRY/SPRY domains. We summarise the current knowledge concerning the mechanism of RNA binding by TRIM proteins and its biological role. We discuss how RNA-binding relates to their previously described functions such as E3 ubiquitin ligase activity, and we will consider the potential role of enrichment in membrane-less organelles.