Hydrolytic endonucleolytic ribozyme (HYER) is programmable for sequence-specific DNA cleavage

Capping in mRNA analyzed using Pistol ribozyme and LC-MS

Understanding and meticulously controlling mRNA capping efficiency is an indispensable quality attribute in developing mRNA therapeutics. A rigorously defined capping process is critical for ensuring the consistency and reproducibility of mRNA drugs, forming the cornerstone of compliance with stringent regulatory standards. This investigation introduces an innovative methodology for assessing mRNA's capping efficiency through applying the Pistol ribozyme and liquid chromatography-mass spectrometry (LC-MS). The capping process, pivotal for mRNA stability and translational efficiency, significantly influences mRNA molecules' immunogenic properties and overall therapeutic efficacy. Our method employs the Pistol ribozyme for precise, site-specific mRNA cleavage, which LC-MS subsequently analyzes to distinguish between capped and uncapped forms. This approach exceeds the capabilities of traditional methods, such as radiolabeling and enzyme-linked immunosorbent assay (ELISA), in specificity and sensitivity, thus enhancing the analysis of mRNA modifications. Our findings confirm the presence of specific cap structures and quantify the efficiency of the mRNA capping process with remarkable accuracy. This advancement drives the development of mRNA-based therapeutics by refining quality control measures and augmenting the effectiveness of vaccines and gene therapies.

Programmable trans-splicing riboregulators for complex cellular logic computation

Synthetic genetic circuits program the cellular input-output relationships to execute customized functions. However, efforts to scale up these circuits have been hampered by the limited number of reliable regulatory mechanisms with high programmability, performance, predictability and orthogonality. Here we report a class of split-intron-enabled trans-splicing riboregulators (SENTRs) based on de novo designed external guide sequences. SENTR libraries provide low leakage expression, wide dynamic range, high predictability with machine learning and low crosstalk at multiple component levels. SENTRs can sense RNA targets, process signals by logic computation and transduce them into various outputs, either mRNAs or noncoding RNAs. We subsequently demonstrate that digital logic operation with up to six inputs can be implemented using multiple orthogonal SENTRs to regulate a single gene simultaneously and coupling SENTRs with split intein-mediated protein trans-splicing. SENTR represents a powerful and versatile regulatory tool at the post-transcriptional level in Escherichia coli, suggesting broad biotechnological applications.

Cryo-EM reveals mechanisms of natural RNA multivalency

Homo-oligomerization of biological macromolecules leads to functional assemblies that are critical to understanding various cellular processes. However, RNA quaternary structures have rarely been reported. Comparative genomics analysis has identified RNA families containing hundreds of sequences that adopt conserved secondary structures and likely fold into complex three-dimensional structures. In this study, we used cryo-electron microscopy (cryo-EM) to determine structures from four RNA families, including ARRPOF and OLE forming dimers and ROOL and GOLLD forming hexameric, octameric, and dodecameric nanostructures, at 2.6- to 4.6-angstrom resolutions. These homo-oligomeric assemblies reveal a plethora of structural motifs that contribute to RNA multivalency, including kissing-loop, palindromic base-pairing, A-stacking, metal ion coordination, pseudoknot, and minor-groove interactions. These results provide the molecular basis of intermolecular interactions driving RNA multivalency with potential functional relevance.

RNA sample optimization for cryo-EM analysis

RNAs play critical roles in most biological processes. Although the three-dimensional (3D) structures of RNAs primarily determine their functions, it remains challenging to experimentally determine these 3D structures due to their conformational heterogeneity and intrinsic dynamics. Cryogenic electron microscopy (cryo-EM) has recently played an emerging role in resolving dynamic conformational changes and understanding structure-function relationships of RNAs including ribozymes, riboswitches and bacterial and viral noncoding RNAs. A variety of methods and pipelines have been developed to facilitate cryo-EM structure determination of challenging RNA targets with small molecular weights at subnanometer to near-atomic resolutions. While a wide range of conditions have been used to prepare RNAs for cryo-EM analysis, correlations between the variables in these conditions and cryo-EM visualizations and reconstructions remain underexplored, which continue to hinder optimizations of RNA samples for high-resolution cryo-EM structure determination. Here we present a protocol that describes rigorous screenings and iterative optimizations of RNA preparation conditions that facilitate cryo-EM structure determination, supplemented by cryo-EM data processing pipelines that resolve RNA dynamics and conformational changes and RNA modeling algorithms that generate atomic coordinates based on moderate- to high-resolution cryo-EM density maps. The current protocol is designed for users with basic skills and experience in RNA biochemistry, cryo-EM and RNA modeling. The expected time to carry out this protocol may range from 3 days to more than 3 weeks, depending on the many variables described in the protocol. For particularly challenging RNA targets, this protocol could also serve as a starting point for further optimizations.

OMEGA-guided DNA polymerases enable random mutagenesis in a tunable window

Targeted random mutagenesis is crucial for breeding, directed evolution, and gene function studies, yet efficient tools remain scarce. Here, we present obligate mobile element guided activity (OMEGA)-R, an innovative targeted random mutagenesis system that integrates SpyCatcher-enIscB and PolI3M-TBD-SpyTag, outperforming existing state-of-the-art technologies in key metrics, such as protein size, mutagenesis efficiency, window length, and continuity. OMEGA-R achieves a dramatic enhancement of on-target mutagenesis, reaching a rate of 1.4 × 10-5 base pairs (bp) per generation (bpg), with minimal off-target effects, in both Escherichia coli and Bacillus subtilis. The system also demonstrates exceptional compatibility with high-throughput screening (HTS) technologies, including fluorescence-activated droplet sorting (FADS) and phage-assisted continuous evolution (PACE). Utilizing OMEGA-R, we successfully identified a series of effective mutations within the T7 promoter (pT7), ribosome-binding site (RBS), superfolder GFP (sfGFP), and autocyclizing ribozyme (AR), which are invaluable for the development of high-performance biotechnology tools. These findings underscore the high efficiency and broad application potential of OMEGA-R.

Hydrolytic endonucleolytic ribozyme (HYER): Systematic identification, characterization and potential application in nucleic acid manipulation

Group II introns are transposable elements that can propagate in host genomes through the "copy and paste" mechanism. They usually comprise RNA and protein components for effective propagation. Recently, we found that some bacterial GII-C introns without protein components had multiple copies in their resident genomes, implicating their potential transposition activity. We demonstrated that some of these systems are active for hydrolytic DNA cleavage and proved their DNA manipulation capability in bacterial or mammalian cells. These introns are therefore named HYdrolytic Endonucleolytic Ribozymes (HYERs). Here, we provide a detailed protocol for the systematic identification and characterization of HYERs and present our perspectives on its potential application in nucleic acid manipulation.

Structures of a natural circularly permuted group II intron reveal mechanisms of branching and backsplicing

Circularly permuted (CP) group II introns, identified in various bacteria phyla, swap domains D5 and D6 near the 5' end and have reversed splice sites (SSs), leading to backsplicing and circular RNA formation. In this study, we present multiple high-resolution cryo-electron microscopy structures of a natural CP group II intron from Comamonas testosteroni KF-1 (Cte 1), elucidating the molecular mechanisms of branching and backsplicing. During branching, the 5' SS is positioned by an auxiliary sequence (AUX)-enhanced interaction between the exon-binding site and intron-binding site (IBS) and stacks on the branch-site adenosine within D6, allowing the attacking 2'-OH group to coordinate with a metal ion in the active center. In backsplicing, the 3' SS is aligned with the branching step, leaving IBS in the active center, stabilized by base pairing with the AUX, which enables the free 3'-end hydroxyl group to directly attack the scissile phosphate of 3' SS. Furthermore, a groove in Cte 1 may stabilize the circular RNA. These findings highlight a conserved catalytic mechanism for canonical group II introns, albeit facilitated by the versatile AUX, opening avenues for designing potent ribozymes producing circular RNAs.

A Manual for Genome and Transcriptome Engineering

Genome and transcriptome engineering have emerged as powerful tools in modern biotechnology, driving advancements in precision medicine and novel therapeutics. In this review, we provide a comprehensive overview of the current methodologies, applications, and future directions in genome and transcriptome engineering. Through this, we aim to provide a guide for tool selection, critically analyzing the strengths, weaknesses, and best use cases of these tools to provide context on their suitability for various applications. We explore standard and recent developments in genome engineering, such as base editors and prime editing, and provide insight into tool selection for change of function (knockout, deletion, insertion, substitution) and change of expression (repression, activation) contexts. Advancements in transcriptome engineering are also explored, focusing on established technologies like antisense oligonucleotides (ASOs) and RNA interference (RNAi), as well as recent developments such as CRISPR-Cas13 and adenosine deaminases acting on RNA (ADAR). This review offers a comparison of different approaches to achieve similar biological goals, and consideration of high-throughput applications that enable the probing of a variety of targets. This review elucidates the transformative impact of genome and transcriptome engineering on biological research and clinical applications that will pave the way for future innovations in the field.

Protein-free catalysis of DNA hydrolysis and self-integration by a ribozyme

Group II introns are ancient self-splicing ribozymes and retrotransposons. Though long speculated to have originated before translation, their dependence on intron-encoded proteins for splicing and mobility has cast doubt on this hypothesis. While some group II introns are known to retain part of their catalytic repertoire in the absence of protein cofactors, protein-free complete reverse splicing of a group II intron into a DNA target has never been demonstrated. Here, we demonstrate the complete independence of a group II intron from protein cofactors in all intron-catalyzed reactions. The ribozyme is capable of fully reverse splicing into single-stranded DNA targets in vitro, readily hydrolyzes DNA substrates and is even able to unwind and react with stably duplexed DNA. Our findings make a protein-free origin for group II introns plausible by expanding their known catalytic capabilities beyond what would be needed to survive the transition from RNA to DNA genomes. Furthermore, the intron's capacity to react with both single and double-stranded DNA in conjunction with its expanded sequence recognition may represent a promising starting point for the development of protein-free genomic editing tools.

Functional RNA mining using random high-throughput screening

Functional RNA participates in various life processes in cells. However, there is currently a lack of effective methods to screen for functional RNA. Here, we developed a technology named random high-throughput screening (rHTS). rHTS uses a random library of ∼250-nt synthesized RNA fragments, with high uniformity and abundance. These fragments are circularized into circular RNA by an auto-cyclizing ribozyme to improve their stability. Using rHTS, we successfully screened and identified three RNA fragments contributing significantly to the growth of Escherichia coli, one of which possesses coding potential. Moreover, we found that two noncoding RNAs (ncRNAs) effectively inhibited the growth of E. coli, in vivo rather than in vitro. Subsequently, we applied the rHTS to a coenzyme-dependent screening platform. In this context, two ncRNAs were identified that could effectively promote the conversion from NADPH to NADP+. Exogenous expression of these two ncRNAs was able to increase the conversion rate of glycerol dehydrogenase from glycerol to 1,3-dihydroxyacetone from 18.3% to 21.8% and 23.2%, respectively. These results suggest that rHTS is a powerful technology for functional RNA mining.

Structure and catalytic activity of the SAM-utilizing ribozyme SAMURI

Ribozymes that catalyze site-specific RNA modification have recently gained increasing interest for their ability to mimic methyltransferase enzymes and for their application to install molecular tags. Recently, we reported SAMURI as a site-specific alkyltransferase ribozyme using S-adenosylmethionine (SAM) or a stabilized analog to transfer a methyl or propargyl group to N3 of an adenosine. Here, we report the crystal structures of SAMURI in the postcatalytic state. The structures reveal a three-helix junction with the catalytic core folded into four stacked layers, harboring the cofactor and the modified nucleotide. Detailed structure-activity analyses explain the cofactor scope and the structural basis for site selectivity. A structural comparison of SAMURI with SAM riboswitches sheds light on how the synthetic ribozyme overcomes the strategies of natural riboswitches to avoid self-methylation. Our results suggest that SAM and its analogs may serve as substrates for various RNA-catalyzed reactions, for which the corresponding ribozymes remain to be identified.

CRISPR-powered RNA sensing in vivo

RNA sensing in vivo evaluates past or ongoing endogenous RNA disturbances, which is crucial for identifying cell types and states and diagnosing diseases. Recently, the CRISPR-driven genetic circuits have offered promising solutions to burgeoning challenges in RNA sensing. This review delves into the cutting-edge developments of CRISPR-powered RNA sensors in vivo, reclassifying these RNA sensors into four categories based on their working mechanisms, including programmable reassembly of split single-guide RNA (sgRNA), RNA-triggered RNA processing and protein cleavage, miRNA-triggered RNA interference (RNAi), and strand displacement reactions. Then, we discuss the advantages and challenges of existing methodologies in diverse application scenarios and anticipate and analyze obstacles and opportunities in forthcoming practical implementations.

Cryo-EM: A window into the dynamic world of RNA molecules

RNAs are critical for complex cellular functions, characterized by their structural versatility and ability to undergo conformational transitions in response to cellular cues. The elusive structures of RNAs are being unraveled with unprecedented clarity, thanks to the technological advancements in structural biology, including nuclear magnetic resonance (NMR), X-ray crystallography, cryo-electron microscopy (cryo-EM) etc. This review focuses on examining the revolutionary impact of cryo-EM on our comprehension of RNA structural dynamics, underscoring the technique's contributions to structural biology and envisioning the future trajectory of this rapidly evolving field.

Advancements in gene editing technologies for probiotic-enabled disease therapy

Probiotics typically refer to microorganisms that have been identified for their health benefits, and they are added to foods or supplements to promote the health of the host. A growing number of probiotic strains have been identified lately and developed into valuable regulatory pharmaceuticals for nutritional and medical applications. Gene editing technologies play a crucial role in addressing the need for safe and therapeutic probiotics in disease treatment. These technologies offer valuable assistance in comprehending the underlying mechanisms of probiotic bioactivity and in the development of advanced probiotics. This review aims to offer a comprehensive overview of gene editing technologies applied in the engineering of both traditional and next-generation probiotics. It further explores the potential for on-demand production of customized products derived from enhanced probiotics, with a particular emphasis on the future of gene editing in the development of live biotherapeutics.

Exploiting viral vectors to deliver genome editing reagents in plants

Genome editing holds great promise for the molecular breeding of plants, yet its application is hindered by the shortage of simple and effective means of delivering genome editing reagents into plants. Conventional plant transformation-based methods for delivery of genome editing reagents into plants often involve prolonged tissue culture, a labor-intensive and technically challenging process for many elite crop cultivars. In this review, we describe various virus-based methods that have been employed to deliver genome editing reagents, including components of the CRISPR/Cas machinery and donor DNA for precision editing in plants. We update the progress in these methods with recent successful examples of genome editing achieved through virus-based delivery in different plant species, highlight the advantages and limitations of these delivery approaches, and discuss the remaining challenges.

Unity among the diverse RNA-guided CRISPR-Cas interference mechanisms

CRISPR-Cas (clustered regularly interspaced short palindromic repeats-CRISPR-associated) systems are adaptive immune systems that protect bacteria and archaea from invading mobile genetic elements (MGEs). The Cas protein-CRISPR RNA (crRNA) complex uses complementarity of the crRNA "guide" region to specifically recognize the invader genome. CRISPR effectors that perform targeted destruction of the foreign genome have emerged independently as multi-subunit protein complexes (Class 1 systems) and as single multi-domain proteins (Class 2). These different CRISPR-Cas systems can cleave RNA, DNA, and protein in an RNA-guided manner to eliminate the invader, and in some cases, they initiate programmed cell death/dormancy. The versatile mechanisms of the different CRISPR-Cas systems to target and destroy nucleic acids have been adapted to develop various programmable-RNA-guided tools and have revolutionized the development of fast, accurate, and accessible genomic applications. In this review, we present the structure and interference mechanisms of different CRISPR-Cas systems and an analysis of their unified features. The three types of Class 1 systems (I, III, and IV) have a conserved right-handed helical filamentous structure that provides a backbone for sequence-specific targeting while using unique proteins with distinct mechanisms to destroy the invader. Similarly, all three Class 2 types (II, V, and VI) have a bilobed architecture that binds the RNA-DNA/RNA hybrid and uses different nuclease domains to cleave invading MGEs. Additionally, we highlight the mechanistic similarities of CRISPR-Cas enzymes with other RNA-cleaving enzymes and briefly present the evolutionary routes of the different CRISPR-Cas systems.