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Tatsuaki Kurosaki, Wencheng Li, Mainul Hoque, Maximilian W-L Popp, Dmitri N Ermolenko, Bin Tian, Lynne E Maquat
Nonsense-mediated mRNA decay (NMD) controls the quality of eukaryotic gene expression and also degrades physiologic mRNAs. How NMD targets are identified is incompletely understood. A central NMD factor is the ATP-dependent RNA helicase upframeshift 1 (UPF1). Neither the distance in space between the termination codon and the poly(A) tail nor the binding of steady-state, largely hypophosphorylated UPF1 is a discriminating marker of cellular NMD targets, unlike for premature termination codon (PTC)-containing reporter mRNAs when compared with their PTC-free counterparts...
September 1, 2014: Genes & Development
Sutapa Chakrabarti, Fabien Bonneau, Steffen Schüssler, Elfriede Eppinger, Elena Conti
Nonsense-mediated mRNA decay (NMD) is a eukaryotic surveillance pathway that recognizes mRNAs with premature stop codons and targets them for rapid degradation. Evidence from previous studies has converged on UPF1 as the central NMD factor. In human cells, the SMG1 kinase phosphorylates UPF1 at the N-terminal and C-terminal tails, in turn allowing the recruitment of the NMD factors SMG5, SMG6 and SMG7. To understand the molecular mechanisms, we recapitulated these steps of NMD in vitro using purified components...
August 2014: Nucleic Acids Research
Stefanie Metze, Veronika A Herzog, Marc-David Ruepp, Oliver Mühlemann
Nonsense-mediated mRNA decay (NMD) is a eukaryotic post-transcriptional gene regulation mechanism that eliminates mRNAs with the termination codon (TC) located in an unfavorable environment for efficient translation termination. The best-studied NMD-targeted mRNAs contain premature termination codons (PTCs); however, NMD regulates even many physiological mRNAs. An exon-junction complex (EJC) located downstream from a TC acts as an NMD-enhancing signal, but is not generally required for NMD. Here, we compared these "EJC-enhanced" and "EJC-independent" modes of NMD with regard to their requirement for seven known NMD factors in human cells using two well-characterized NMD reporter genes (immunoglobulin μ and β-Globin) with or without an intron downstream from the PTC...
October 2013: RNA
Hana Cho, Sisu Han, Junho Choe, Seung Gu Park, Sun Shim Choi, Yoon Ki Kim
In mammals, nonsense-mediated mRNA decay (NMD) functions in post-transcriptional gene regulation as well as mRNA surveillance. A key NMD factor, Upf1, becomes hyperphosphorylated by SMG1 kinase during the recognition of NMD substrates. Hyperphosphorylated Upf1 interacts with several factors including SMG5, SMG6, SMG7 and PNRC2 to trigger rapid mRNA degradation. However, the possible cross-talk among these factors and their selective use during NMD remain unknown. Here, we show that PNRC2 is preferentially complexed with SMG5, but not with SMG6 or SMG7, and that downregulation of PNRC2 abolishes the interaction between SMG5 and Dcp1a, a component of the decapping complex...
January 2013: Nucleic Acids Research
Nadine Wittkopp, Eric Huntzinger, Catrin Weiler, Jérôme Saulière, Steffen Schmidt, Mahendra Sonawane, Elisa Izaurralde
The nonsense-mediated mRNA decay (NMD) pathway promotes rapid degradation of mRNAs containing premature translation termination codons (PTCs or nonsense codons), preventing accumulation of potentially detrimental truncated proteins. In metazoa, seven genes (upf1, upf2, upf3, smg1, smg5, smg6, and smg7) have been identified as essential for NMD; here we show that the zebrafish genome encodes orthologs of upf1, upf2, smg1, and smg5 to smg7 and two upf3 paralogs. We also show that Upf1 is required for degradation of PTC-containing mRNAs in zebrafish embryos...
July 2009: Molecular and Cellular Biology
Claus M Azzalin, Joachim Lingner
The eukaryotic nonsense-mediated mRNA decay (NMD) pathway degrades mRNAs carrying premature stop codons (PTC). In humans, NMD depends on the RNA- and DNA-dependent 5'-3' helicase UPF1 and six other gene products referred to as SMG1, UPF2, UPF3, EST1A/SMG6, EST1B/SMG5, and EST1C/SMG7. The NMD machinery is also thought to coordinate mRNA nuclear export and translation and to regulate the levels of several physiologic transcripts. Furthermore, in a process named SMD, UPF1 promotes degradation of mRNAs that are bound by Staufen 1...
February 21, 2006: Current Biology: CB
David Gatfield, Leonie Unterholzner, Francesca D Ciccarelli, Peer Bork, Elisa Izaurralde
The nonsense-mediated mRNA decay (NMD) pathway promotes the rapid degradation of mRNAs containing premature stop codons (PTCs). In Caenorhabditis elegans, seven genes (smg1-7) playing an essential role in NMD have been identified. Only SMG2-4 (known as UPF1-3) have orthologs in Saccharomyces cerevisiae. Here we show that the Drosophila orthologs of UPF1-3, SMG1, SMG5 and SMG6 are required for the degradation of PTC-containing mRNAs, but that there is no SMG7 ortholog in this organism. In contrast, orthologs of SMG5-7 are encoded by the human genome and all three are required for NMD...
August 1, 2003: EMBO Journal
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