title: SMG6 promotes endonucleolytic cleavage of nonsense mRNA in human cells.
abstract: From yeast to humans, mRNAs harboring premature termination codons (PTCs) are recognized and degraded by nonsense-mediated mRNA decay (NMD). However, degradation mechanisms of NMD have been suggested to differ between species. In Drosophila melanogaster, NMD is initiated by endonucleolysis near the PTC, whereas in yeast and human cells the current view posits that NMD occurs by exonucleolysis from one or both RNA termini. Here we report that degradation of human nonsense mRNAs can be initiated by PTC-proximal endonucleolytic cleavage. We identify the metazoan-specific NMD factor SMG6 as the responsible endonuclease by demonstrating that mutation of conserved residues in its nuclease domain--the C-terminal PIN motif--abolishes endonucleolysis in vivo and in vitro. Our data lead to a revised mechanistic model for degradation of nonsense mRNA in human cells and suggest that endonucleolytic cleavage is a conserved feature in metazoan NMD.
authors.affiliation: Institute of Cell Biology, University of Bern, Baltzerstrasse 4, CH-3012 Bern, Switzerland.
authors.forename: Andrea B
authors.initials: AB
authors.lastname: Eberle
authors.forename: Søren
authors.initials: S
authors.lastname: Lykke-Andersen
authors.forename: Oliver
authors.initials: O
authors.lastname: Mühlemann
authors.forename: Torben Heick
authors.initials: TH
authors.lastname: Jensen
mesh_terms: D000818:Animals; D003062:Codon / Q000235:genetics; D018389:Codon, Nonsense; D017124:Conserved Sequence; D017931:DNA Primers; D004331:Drosophila melanogaster / Q000235:genetics; D005091:Exons; D019674:Genes, T-Cell Receptor beta; D006801:Humans; D017354:Point Mutation; D034622:RNA Interference; D012333:RNA, Messenger / Q000737:chemistry / Q000235:genetics*; D019098:Telomerase / Q000235:genetics* / Q000378:metabolism; D013728:Terminator Regions, Genetic / Q000235:genetics; D014158:Transcription, Genetic; D055544:beta-Globins / Q000235:genetics; D004722:Endoribonucleases
chemical_list: D003062:Codon; D018389:Codon, Nonsense; D017931:DNA Primers; D012333:RNA, Messenger; D019098:Telomerase; D055544:beta-Globins; C512261:SMG6 protein, human; D004722:Endoribonucleases