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Molecular mechanisms governing the formation of distinct Upf1-containing complexes in yeast

ABSTRACT: Upf1 is a master regulator of nonsense-mediated mRNA decay (NMD), an mRNA surveillance and degradation pathway conserved from yeast to human. In S. cerevisiae, Upf1 exists in two distinct complexes with factors that mediate NMD activation or 5'-3' mRNA degradation. We combined endogenous purifications and biochemical reconstitutions of yeast Upf1 complexes with structural analyses and biochemical assays to elucidate the molecular mechanisms driving the mutually exclusive organization of the Upf1-5'-3' and Upf1-2-3 complexes. We show that yeast Upf1 is in a constitutive complex whereby its CH, RecA and C-terminal domains interact with the mRNA decapping factor Dcp2, NMD-associated proteins Nmd4 and Ebs1, and the 5'-3' exoribonuclease Xrn1, respectively. Together, the interacting surfaces and closed conformation of Upf1 in the Upf1-5'-3' complex sterically obstruct the binding of Upf2-3. Our work points to a major restructuring upon recruitment of these factors during NMD and provides insights into evolutionary divergence amongst species.

ORGANISM(S): Saccharomyces cerevisiae

PROVIDER: GSE307461 | GEO | 2025/10/15

REPOSITORIES: GEO

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Molecular mechanisms governing the formation of distinct Upf1-containing complexes in yeast

Project description:Upf1 is a master regulator of nonsense-mediated mRNA decay (NMD), an mRNA surveillance and degradation pathway conserved from yeast to human. In S. cerevisiae, Upf1 exists in two distinct complexes with factors that mediate NMD activation or 5'-3' mRNA degradation. We combined endogenous purifications and biochemical reconstitutions of yeast Upf1 complexes with structural analyses and biochemical assays to elucidate the molecular mechanisms driving the mutually exclusive organization of the Upf1-5'-3' and Upf1-2-3 complexes. We show that yeast Upf1 is in a constitutive complex whereby its CH, RecA and C-terminal domains interact with the mRNA decapping factor Dcp2, NMD-associated proteins Nmd4 and Ebs1, and the 5' 3' exoribonuclease Xrn1, respectively. Together, the interacting surfaces and closed conformation of Upf1 in the Upf1-5'-3' complex sterically obstruct the binding of Upf2-3. Our work points to a major restructuring upon recruitment of these factors during NMD and provides insights into evolutionary divergence amongst species.

2025-10-14 | PXD068369 | Pride

Quantitative proteomics of affinity purified yeast NMD complexes

Project description:Nonsense-mediated mRNA decay (NMD) is a major translation-dependent RNA degradation pathway required for embryo development and telomere maintenance. Core NMD factors Upf1, Upf2 and Upf3 are conserved from yeast to mammals but a model of the NMD machinery compatible with all eukaryotes is not yet available. We performed the first large-scale quantitative characterization of yeast NMD complexes through affinity purification and mass-spectrometry with 7 different NMD-related factors, with or without Rnase, in strains deleted or not for NMD genes. This extensive characterization of NMD complexes identified two distinct complexes associated with Upf1: Detector (Upf1/2/3) and Effector. Effector contained, in addition to Upf1, the mRNA decapping enzyme and two potential equivalents of mammalian Smg6/5/7: Nmd4 and Ebs1. Like the Smg proteins, Nmd4 and Ebs1 were required for efficient NMD. Our results suggest that the core eukaryotic NMD machinery is conserved across species and operates through successive Upf1-bound Detector and Effector complexes.

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Evaluation of affinity purified RNA-protein complexes related with NMD

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RNAs associated with Upf1, Pab1, Rpl16a, Lsm1 proteins in yeast

Project description:Nonsense mediated mRNA decay (NMD) is a translation-dependent surveillance pathway that eliminates RNAs with short open reading frames (ORFs) and long 3' untranslated regions (UTRs). Upf1 is the key protein of this degradation pathway and we were interested to purify the associated RNAs. Moreover we have done purifications of two proteins from the general mRNA turnover in yeast : Pab1 and Lsm1 that both bind RNAs poly(A) tails. We have also done a purification with a protein from the small ribosomal subunit (40S) in order to have a look at the translated RNAs.

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Project description:Nonsense-mediated mRNA decay (NMD) is a conserved co-translational mRNA surveillance and turnover pathway across eukaryotes. NMD has a central role in degrading defective mRNAs and also regulates the stability of a significant portion of the transcriptome. The pathway is organized around UPF1, an RNA helicase that can interact with several NMD-specific factors. In human cells, degradation of the targeted mRNAs begins with a cleavage event that requires the recruitment of the SMG6 endonuclease to UPF1. Previous studies have identified functional links between SMG6 and UPF1, but the underlying molecular mechanisms have remained elusive. In this work, we used mass spectrometry, structural biology and biochemical approaches to identify and characterize a conserved short linear motif in SMG6 that interacts with the cysteine/histidine-rich (CH) domain of UPF1. Unexpectedly, we found that the UPF1-SMG6 interaction is precluded when the UPF1 CH domain is engaged with another NMD factor, UPF2. Based on cryo-EM data, we propose that the formation of distinct SMG6-containing and UPF2-containing NMD complexes may be dictated by the RNA-binding status of UPF1. Our findings rationalize a key event in the metazoan NMD quality control pathway and progress our understanding of mechanisms regulating activity and guiding substrate recognition by the SMG6 endonuclease.

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Project description:The RNA helicase UPF1 interacts with mRNAs, mRNA decay machinery, and the terminating ribosome to promote nonsense-mediated mRNA decay (NMD). Structural and biochemical data have revealed that UPF1 exists in an enzymatically autoinhibited “closed” state. Upon binding the NMD protein UPF2, UPF1 undergoes an extensive conformational change into a more enzymatically active “open” state, which exhibits enhanced ATPase and helicase activity. However, mechanically deficient UPF1 mutants can support efficient NMD, bringing into question the roles of UPF1 enzymatic autoinhibition and activation in NMD. Here, we identify two additional important features of the activated open state: slower nucleic acid binding kinetics and enhanced ATP-stimulated nucleic acid dissociation kinetics. Computational modeling based on empirical measurements of UPF1, UPF2, and RNA interaction kinetics predicts that the majority of UPF1-RNA binding and dissociation events in cells occur independently of UPF2 binding. We find that UPF1 mutants with either reduced or accelerated dissociation from RNA have NMD defects, whereas UPF1 mutants that are more dependent on UPF2 for catalytic activity remain active on well-established NMD targets. These findings support a model in which the kinetics of UPF1-mRNA interactions are important determinants of cellular NMD efficiency.

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UPF1 ATPase autoinhibition and activation modulate RNA binding kinetics and NMD efficiency 1

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2015-07-06 | E-GEOD-69584 | biostudies-arrayexpress

Target discrimination in nonsense-mediated mRNA decay requires Upf1 ATPase activity (RIP-Seq)

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