Highlights d Structure of SARS-CoV-2 replication-transcription complex (RTC) with nsp13 helicases d The nsp13 NTPase domains sit in front of the RCT, constraining functional models d Nsp13 may drive RTC backtracking, affecting proofreading and template switching d Structural analysis of ADP-Mg 2+-bound NiRAN domain, a potential antiviral target

SUMMARYSARS-CoV-2 is the causative agent of the 2019-2020 pandemic. The SARS-CoV-2 genome is replicated-transcribed by the RNA-dependent RNA polymerase holoenzyme (subunits nsp7/nsp82/nsp12) along with a cast of accessory factors. One of these factors is the nsp13 helicase. Both the holo-RdRp and nsp13 are essential for viral replication and are targets for treating the disease COVID-19. Here we present cryo-electron microscopic structures of the SARS-CoV-2 holo-RdRp with an RNA template-product in complex with two molecules of the nsp13 helicase. The Nidovirus-order-specific N-terminal domains of each nsp13 interact with the N-terminal extension of each copy of nsp8. One nsp13 also contacts the nsp12-thumb. The structure places the nucleic acid-binding ATPase domains of the helicase directly in front of the replicating-transcribing holo-RdRp, constraining models for nsp13 function. We also observe ADP-Mg2+ bound in the nsp12 N-terminal nidovirus RdRp-associated nucleotidyltransferase domain, detailing a new pocket for anti-viral therapeutic development.

Highlights d A1CF regulates alternative splicing of liver-enriched transcripts d A1CF is required for the high-activity ketohexokinase-C (KHK-C) isoform d Antagonistic actions of hnRNPH1/2 and A1CF mediate KHK-A/KHK-C switch d A1CF regulates fructolysis and glucose production in the liver

Fragile X Mental Retardation protein (FMRP), widely known for its role in hereditary intellectual disability, is an RNA-binding protein (RBP) that controls translation of select mRNAs. We discovered that endoplasmic reticulum (ER) stress induces phosphorylation of FMRP on a site that is known to enhance translation inhibition of FMRP-bound mRNAs. We show ER stress-induced activation of Inositol requiring enzyme-1 (IRE1), an ER-resident stress-sensing kinase/endoribonuclease, leads to FMRP phosphorylation and to suppression of macrophage cholesterol efflux and apoptotic cell clearance (efferocytosis). Conversely, FMRP deficiency and pharmacological inhibition of IRE1 kinase activity enhances cholesterol efflux and efferocytosis, reducing atherosclerosis in mice. Our results provide mechanistic insights into how ER stress-induced IRE1 kinase activity contributes to macrophage cholesterol homeostasis and suggests IRE1 inhibition as a promising new way to counteract atherosclerosis.