title: Characterization of SMG-9, an essential component of the nonsense-mediated mRNA decay SMG1C complex.
abstract: SMG-9 is part of a protein kinase complex, SMG1C, which consists of the SMG-1 kinase, SMG-8 and SMG-9. SMG1C mediated phosphorylation of Upf1 triggers nonsense-mediated mRNA decay (NMD), a eukaryotic surveillance pathway that detects and targets for degradation mRNAs harboring premature translation termination codons. Here, we have characterized SMG-9, showing that it comprises an N-terminal 180 residue intrinsically disordered region (IDR) followed by a well-folded C-terminal domain. Both domains are required for SMG-1 binding and the integrity of the SMG1C complex, whereas the C-terminus is sufficient to interact with SMG-8. In addition, we have found that SMG-9 assembles in vivo into SMG-9:SMG-9 and, most likely, SMG-8:SMG-9 complexes that are not constituents of SMG1C. SMG-9 self-association is driven by interactions between the C-terminal domains and surprisingly, some SMG-9 oligomers are completely devoid of SMG-1 and SMG-8. We propose that SMG-9 has biological functions beyond SMG1C, as part of distinct SMG-9-containing complexes. Some of these complexes may function as intermediates potentially regulating SMG1C assembly, tuning the activity of SMG-1 with the NMD machinery. The structural malleability of IDRs could facilitate the transit of SMG-9 through several macromolecular complexes.
authors.affiliation: Centro de Investigaciones Biológicas, Consejo Superior de Investigaciones Científicas (CSIC), Ramiro de Maetzu 9, 28040 Madrid, Spain.
authors.forename: Israel S
authors.initials: IS
authors.lastname: Fernández
authors.forename: Akio
authors.initials: A
authors.lastname: Yamashita
authors.forename: Ernesto
authors.initials: E
authors.lastname: Arias-Palomo
authors.forename: Yumi
authors.initials: Y
authors.lastname: Bamba
authors.forename: Ruben A
authors.initials: RA
authors.lastname: Bartolomé
authors.forename: M Angeles
authors.initials: MA
authors.lastname: Canales
authors.forename: Joaquín
authors.initials: J
authors.lastname: Teixidó
authors.forename: Shigeo
authors.initials: S
authors.lastname: Ohno
authors.forename: Oscar
authors.initials: O
authors.lastname: Llorca
mesh_terms: D018389:Codon, Nonsense; D006367:HeLa Cells; D006801:Humans; D055503:Protein Multimerization; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D021122:Protein Subunits / Q000737:chemistry* / Q000378:metabolism; D020871:RNA Stability; D012333:RNA, Messenger / Q000378:metabolism
chemical_list: D018389:Codon, Nonsense; D021122:Protein Subunits; D012333:RNA, Messenger; D017346:Protein Serine-Threonine Kinases
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