N 6 -methyladenosine (m 6 A) is an abundant internal RNA modification, influencing transcript fate and function in uninfected and virus-infected cells. Installation of m 6 A by the nuclear RNA methyltransferase METTL3 occurs cotranscriptionally; however, the genomes of some cytoplasmic RNA viruses are also m 6 A-modified. How the cellular m 6 A modification machinery impacts coronavirus replication, which occurs exclusively in the cytoplasm, is unknown. Here we show that replication of SARS-CoV-2, the agent responsible for the COVID-19 pandemic, and a seasonal human β-coronavirus HCoV-OC43, can be suppressed by depletion of METTL3 or cytoplasmic m 6 A reader proteins YTHDF1 and YTHDF3 and by a highly specific small molecule METTL3 inhibitor. Reduction of infectious titer correlates with decreased synthesis of viral RNAs and the essential nucleocapsid (N) protein. Sites of m 6 A modification on genomic and subgenomic RNAs of both viruses were mapped by methylated RNA immunoprecipitation sequencing (meRIP-seq). Levels of host factors involved in m 6 A installation, removal, and recognition were unchanged by HCoV-OC43 infection; however, nuclear localization of METTL3 and cytoplasmic m 6 A readers YTHDF1 and YTHDF2 increased. This establishes that coronavirus RNAs are m 6 A-modified and host m 6 A pathway components control β-coronavirus replication. Moreover, it illustrates the therapeutic potential of targeting the m 6 A pathway to restrict coronavirus reproduction.

Adenovirus is a nuclear replicating DNA virus reliant on host RNA processing machinery. Processing and metabolism of cellular RNAs can be regulated by METTL3, which catalyzes the addition of N6-methyladenosine (m6A) to mRNAs. While m6A-modified adenoviral RNAs have been previously detected, the location and function of this mark within the infectious cycle is unknown. Since the complex adenovirus transcriptome includes overlapping spliced units that would impede accurate m6A mapping using short-read sequencing, here we profile m6A within the adenovirus transcriptome using a combination of meRIP-seq and direct RNA long-read sequencing to yield both nucleotide and transcript-resolved m6A detection. Although both early and late viral transcripts contain m6A, depletion of m6A writer METTL3 specifically impacts viral late transcripts by reducing their splicing efficiency. These data showcase a new technique for m6A discovery within individual transcripts at nucleotide resolution, and highlight the role of m6A in regulating splicing of a viral pathogen.

N6-methyladenosine (m6A) is the most abundant internal messenger RNA (mRNA) modification, contributing to the processing, stability, and function of methylated RNAs. Methylation occurs in the nucleus during pre-mRNA synthesis and requires a core methyltransferase complex consisting of METTL3, METTL14, and WTAP. During herpes simplex virus (HSV-1) infection, cellular gene expression is profoundly suppressed, allowing the virus to monopolize the host transcription and translation apparatus and antagonize antiviral responses. The extent to which HSV-1 uses or manipulates the m6A pathway is not known. Here, we show that, in primary fibroblasts, HSV-1 orchestrates a striking redistribution of the nuclear m6A machinery that progresses through the infection cycle. METTL3 and METTL14 are dispersed into the cytoplasm, whereas WTAP remains nuclear. Other regulatory subunits of the methyltransferase complex, along with the nuclear m6A-modified RNA binding protein YTHDC1 and nuclear demethylase ALKBH5, are similarly redistributed. These changes require ICP27, a viral regulator of host mRNA processing that mediates the nucleocytoplasmic export of viral late mRNAs. Viral gene expression is initially reduced by small interfering RNA (siRNA)-mediated inactivation of the m6A methyltransferase but becomes less impacted as the infection advances. Redistribution of the nuclear m6A machinery is accompanied by a wide-scale reduction in the installation of m6A and other RNA modifications on both host and viral mRNAs. These results reveal a far-reaching mechanism by which HSV-1 subverts host gene expression to favor viral replication.

Motivation The chemical modification of ribonucleotides regulates the structure, stability, and interactions of RNAs. Profiling of these modifications using short-read (Illumina) sequencing techniques provides high sensitivity but low-to-medium resolution i.e., modifications cannot be assigned to specific transcript isoforms in regions of sequence overlap. An alternative strategy uses current fluctuations in nanopore-based long read direct RNA sequencing (DRS) to infer the location and identity of nucleotides that differ between two experimental conditions. While highly sensitive, these signal-level analyses require high quality transcriptome annotations and thus are best suited to the study of model organisms. By contrast, the detection of RNA modifications in microbial organisms which typically have no or low-quality annotations requires an alternative strategy. Here, we demonstrate that signal fluctuations directly influence error rates during base calling and thus provides an alternative approach for identifying modified nucleotides. Results DRUMMER (Detection of Ribonucleic acid Modifications Manifested in Error Rates (i) utilizes a range of statistical tests and background noise correction to identify modified nucleotides with high confidence, (ii) operates with similar sensitivity to signal-level analysis approaches, and (iii) correlates very well with orthogonal approaches. Using well-characterized DRS datasets supported by independent meRIP-Seq and miCLIP-Seq datasets we demonstrate that DRUMMER operates with high sensitivity and specificity. Availability and implementation DRUMMER is written in Python 3 and is available as open source in the GitHub repository: https://github.com/DepledgeLab/DRUMMER Supplementary information Supplementary data are available at Bioinformatics online.

The chemical modification of ribonucleotides plays an integral role in the biology of diverse viruses and their eukaryotic host cells. Mapping the precise identity, location, and abundance of modified ribonucleotides remains a key goal of many studies aimed at characterizing the function and importance of a given modification.

CRISPR/Cas9-mediated genome editing in mammalian cells can generate undesired chromosomal alterations, including deleterious on-target large deletions and chromosomal translocations. Currently few approaches effectively prevent these on-target DNA damage. Here we show that the association of engineered phage DNA polymerases with Cas9 protein substantially inhibits the production of undesired on-target chromosomal alterations. Our "CasPlus" editing platform significantly increases the proportion of precise 1- to 3-base-pair insertions at target sites. CasPlus efficiently corrected common mutations in the DMD (del exon 52) and CFTR (F508del) genes by generating precise insertions without an exogenous template with fewer deleterious edits than Cas9 alone. CasPlus offers safer and more efficient targeting strategies optimized for human applications.