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Nucleic Acids Res. 2014 Feb;42(4):2673-86. doi: 10.1093/nar/gkt1197. Epub 2013 Nov 23.

Structural and functional analysis of the three MIF4G domains of nonsense-mediated decay factor UPF2.

Author information

1
European Molecular Biology Laboratory, Grenoble Outstation, 6 rue Jules Horowitz, 38042 Grenoble Cedex 9, France, Unit of Virus Host-Cell Interactions, University of Grenoble Alpes-EMBL-CNRS, UMI 3265, 6 rue Jules Horowitz, 38042 Grenoble Cedex 9, France and University of Cologne, Institute for Genetics, Zuelpicher Street 47a, 50674 Cologne, Germany.

Abstract

Nonsense-mediated decay (NMD) is a eukaryotic quality control pathway, involving conserved proteins UPF1, UPF2 and UPF3b, which detects and degrades mRNAs with premature stop codons. Human UPF2 comprises three tandem MIF4G domains and a C-terminal UPF1 binding region. MIF4G-3 binds UPF3b, but the specific functions of MIF4G-1 and MIF4G-2 are unknown. Crystal structures show that both MIF4G-1 and MIF4G-2 contain N-terminal capping helices essential for stabilization of the 10-helix MIF4G core and that MIF4G-2 interacts with MIF4G-3, forming a rigid assembly. The UPF2/UPF3b/SMG1 complex is thought to activate the kinase SMG1 to phosphorylate UPF1 in vivo. We identify MIF4G-3 as the binding site and in vitro substrate of SMG1 kinase and show that a ternary UPF2 MIF4G-3/UPF3b/SMG1 complex can form in vitro. Whereas in vivo complementation assays show that MIF4G-1 and MIF4G-2 are essential for NMD, tethering assays reveal that UPF2 truncated to only MIF4G-3 and the UPF1-binding region can still partially accomplish NMD. Thus UPF2 MIF4G-1 and MIF4G-2 appear to have a crucial scaffolding role, while MIF4G-3 is the key module required for triggering NMD.

PMID:
24271394
PMCID:
PMC3936715
DOI:
10.1093/nar/gkt1197
[Indexed for MEDLINE]
Free PMC Article
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