1. Coupled 5′ Nucleotide Recognition and Processivity in Xrn1-Mediated mRNA Decay
- Author
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Jinek, Martin, Coyle, Scott M, and Doudna, Jennifer A
- Subjects
Biochemistry and Cell Biology ,Biological Sciences ,Genetics ,1.1 Normal biological development and functioning ,Animals ,Catalysis ,Drosophila Proteins ,Drosophila melanogaster ,Exoribonucleases ,Hydrolysis ,Magnesium ,Mutation ,Nucleic Acid Conformation ,Nucleotides ,Phosphates ,Phosphorylation ,Protein Conformation ,Protein Structure ,Tertiary ,RNA ,Messenger ,Medical and Health Sciences ,Developmental Biology ,Biological sciences ,Biomedical and clinical sciences ,Health sciences - 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.
- Published
- 2011