title: Coupled 5' nucleotide recognition and processivity in Xrn1-mediated mRNA decay.
abstract: Messenger RNA decay plays a central role in the regulation and surveillance of eukaryotic gene expression. The conserved multidomain exoribonuclease Xrn1 targets cytoplasmic RNA substrates marked by a 5' monophosphate for processive 5'-to-3' degradation by an unknown mechanism. Here, we report the crystal structure of an Xrn1-substrate complex. The single-stranded substrate is held in place by stacking of the 5'-terminal trinucleotide between aromatic side chains while a highly basic pocket specifically recognizes the 5' phosphate. Mutations of residues involved in binding the 5'-terminal nucleotide impair Xrn1 processivity. The substrate recognition mechanism allows Xrn1 to couple processive hydrolysis to duplex melting in RNA substrates with sufficiently long single-stranded 5' overhangs. The Xrn1-substrate complex structure thus rationalizes the exclusive specificity of Xrn1 for 5'-monophosphorylated substrates, ensuring fidelity of mRNA turnover, and posits a model for translocation-coupled unwinding of structured RNA substrates.
authors.affiliation: Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720, USA.
authors.forename: Martin
authors.initials: M
authors.lastname: Jinek
authors.forename: Scott M
authors.initials: SM
authors.lastname: Coyle
authors.forename: Jennifer A
authors.initials: JA
authors.lastname: Doudna
mesh_terms: D000818:Animals; D002384:Catalysis; D029721:Drosophila Proteins / Q000235:genetics*; D004331:Drosophila melanogaster; D005095:Exoribonucleases / Q000235:genetics*; D006868:Hydrolysis; D008274:Magnesium / Q000737:chemistry; D009154:Mutation; D009690:Nucleic Acid Conformation; D009711:Nucleotides / Q000235:genetics*; D010710:Phosphates / Q000737:chemistry; D010766:Phosphorylation; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D012333:RNA, Messenger / Q000378:metabolism*
chemical_list: D029721:Drosophila Proteins; D009711:Nucleotides; D010710:Phosphates; D012333:RNA, Messenger; D005095:Exoribonucleases; C487208:pcm protein, Drosophila; D008274:Magnesium