Nucleic Acids Research最新文献

All known bacterial tRNAs adopt the canonical cloverleaf 2D and L-shaped 3D structures. We aimed to explore whether alternative tRNA structures could be introduced in bacterial translation. To this end, we crafted a vitamin-based genetic system to evolve Escherichia coli toward activity of structurally non-canonical tRNAs. The system reliably couples (escape frequency <10-12) growth with the activities of a novel orthogonal histidine suppressor tRNA (HisTUAC) and of the cognate ARS (HisS) via suppression of a GTA valine codon in the mRNA of an enzyme in thiamine biosynthesis (ThiN). Suppression results in the introduction of an essential histidine and thereby confers thiamine prototrophy. We then replaced HisTUAC in the system with non-canonical suppressor tRNAs and selected for growth. A strain evolved to utilize mini HisT, a tRNA lacking the D-arm, and we identified the responsible mutation in an RNase gene (pnp) involved in tRNA degradation. This indicated that HisS, the ribosome, and EF-Tu accept mini HisT ab initio, which we confirmed genetically and through in vitro translation experiments. Our results reveal a previously unknown flexibility of the bacterial translation machinery for the accepted fold of the adaptor of the genetic code and demonstrate the power of the vitamin-based suppression system.

The model organism Escherichia coli K-12 has one of the most extensively annotated genomes in terms of functional characterization, yet a significant number of genes, ∼35%, are still considered poorly characterized. Initially genes without known functional understanding were given 'y' gene names. However, due to inconsistency in changing 'y' names to non-'y' names over the years, gene name alone does not provide sufficient information as to the characterization level of genes. Attempts to characterize y-ome genes, i.e. those that lack experimental evidence for function, are ongoing, and recent categorization based on the level of experimental evidence has helped clarify those genes that are well characterized versus uncharacterized. EcoCyc, the most comprehensive, curated genome database for E. coli K-12 substr. MG1655, has updated this approach by expanding the categories to include Partially characterized genes using a set of computational rules that includes keywords, experimental evidence codes and Gene Ontology terms. Approximately half of the previously categorized y-ome genes are now categorized as Partially characterized, leaving 15.5% (738) as Uncharacterized genes in EcoCyc. This new categorization scheme is searchable in the EcoCyc database, will be updated as new experimental evidence is curated and provides important information for research decisions.

Human replication protein A (RPA) is a heterotrimeric ssDNA binding protein responsible for many aspects of cellular DNA metabolism. Dynamic interactions of the four RPA DNA binding domains (DBDs) with DNA control replacement of RPA by downstream proteins in various cellular metabolic pathways. RPA plays several important functions at telomeres where it binds to and melts telomeric G-quadruplexes, non-canonical DNA structures formed at the G-rich telomeric ssDNA overhangs. Here, we combine single-molecule total internal reflection fluorescence microscopy (smTIRFM) and mass photometry (MP) with biophysical and biochemical analyses to demonstrate that heterogeneous nuclear ribonucleoprotein A1 (hnRNPA1) specifically remodels RPA bound to telomeric ssDNA by dampening the RPA configurational dynamics and forming a ternary complex. Uniquely, among hnRNPA1 target RNAs, telomeric repeat-containing RNA (TERRA) is selectively capable of releasing hnRNPA1 from the RPA-telomeric DNA complex. We speculate that this telomere specific RPA-DNA-hnRNPA1 complex is an important structure in telomere protection.

Molecular staples or interfacial inhibitors are small molecules that exert their activity through co-association with macromolecules leading to various effects on target functions. Some molecules inhibit target activity, while others generate gain-of-function complexes. We and others have previously identified two structurally distinct classes of molecular staples, pateamine A and rocaglates. These molecules inhibit eukaryotic initiation factor (eIF) 4A, a critical RNA helicase required for translation initiation, by simultaneously interacting with both RNA and protein components. Structural insights from members of these two families indicate that they wedge themselves between RNA bases during engagement. To extend our understanding of rocaglates, we investigated the RNA-binding properties of silvestrol, a natural rocaglate distinguished by the presence of a unique dioxanyloxy ring. Our study demonstrates that silvestrol expands the RNA-binding repertoire of rocaglates due to this structural characteristic, providing a rationale for improving synthetic molecular staples targeting eIF4A.

Transcriptome-wide association study (TWAS) has successfully identified numerous complex disease susceptibility genes in the post-genome-wide association study (GWAS) era. Over the past 3 years, the focus of TWAS algorithms has shifted from merely identifying associations to understanding how single nucleotide polymorphisms (SNPs) regulate gene expression, with a growing emphasis on incorporating fine-mapping techniques. Additionally, the rapid increase in GWAS summary statistics, driven largely by the UK Biobank and other consortia, has made it essential to update our webTWAS resource. To address these challenges and meet the growing needs of researchers, we developed webTWAS 2.0, an updated platform for identifying susceptibility genes for human complex diseases using TWAS. Additionally, webTWAS 2.0 provides an online TWAS analysis tool that simplifies conducting TWAS analyses. The updated resource includes 7247 GWAS summary statistics covering 1588 complex human diseases from 192 publications. It also incorporates multiple TWAS methods, such as sTF-TWAS, 3'aTWAS and GIFT, along with an updated interactive visualization tool that allows users to easily explore significant associations across different methods. Other upgrades include a personalized online analysis tool for user-submitted GWAS data and a refined search function that makes it easier to identify relevant associations and meet diverse user needs more efficiently. webTWAS 2.0 is freely accessible at http://www.webtwas.net.

Humans are exposed to DNA alkylating agents through endogenous metabolism, environmental exposure and cancer chemotherapy. The resulting alkylated DNA adducts may elicit genome instability by perturbing DNA replication and transcription. R-loops regulate various cellular processes, including transcription, DNA repair, and telomere maintenance. However, unscheduled R-loops are also recognized as potential sources of DNA damage and genome instability. In this study, by employing fluorescence microscopy and R-loop sequencing approaches, we uncovered, for the first time, that minor-groove N2-alkyl-dG lesions elicit elevated R-loop accumulation in chromatin and in plasmid DNA in cells. We also demonstrated that the N2-alkyl-dG-induced R-loops impede transcription elongation and compromise genome integrity. Moreover, genetic depletion of DDX23, a R-loop helicase, renders cells more sensitive toward benzo[a]pyrene diolepoxide, a carcinogen that induces mainly the minor-groove N2-dG adduct. Together, our work unveiled that unrepaired minor-groove N2-alkyl-dG lesions may perturb genome integrity through augmenting R-loop levels in chromatin. Our findings suggest a potential therapeutic strategy involving the combination of R-loop helicase inhibitors with DNA alkylating drugs.

The essential Drosophila RNA-binding protein Brain Tumor (Brat) represses specific genes to control embryogenesis and differentiation of stem cells. In the brain, Brat functions as a tumor suppressor that diminishes neural stem cell proliferation while promoting differentiation. Though important Brat-regulated target mRNAs have been identified in these contexts, the full impact of Brat on gene expression remains to be discovered. Here, we identify the network of Brat-regulated mRNAs by performing RNA sequencing (RNA-seq) following depletion of Brat from cultured cells. We identify 158 mRNAs, with high confidence, that are repressed by Brat. De novo motif analysis identified a functionally enriched RNA motif in the 3' untranslated regions (UTRs) of Brat-repressed mRNAs that matches the biochemically defined Brat binding site. Integrative data analysis revealed a high-confidence list of Brat-repressed and Brat-bound mRNAs containing 3'UTR Brat binding motifs. Our RNA-seq and reporter assays show that multiple 3'UTR motifs promote the strength of Brat repression, whereas motifs in the 5'UTR are not functional. Strikingly, we find that Brat regulates expression of glycolytic enzymes and the vacuolar ATPase complex, providing new insight into its role as a tumor suppressor and the coordination of metabolism and intracellular pH.