Widespread remodeling of the m6A RNA-modification landscape by a viral regulator of RNA processing and export.

N 6-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.