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Nucleic Acids Res. 2011 Jan;39(1):347-58. doi: 10.1093/nar/gkq749. Epub 2010 Sep 3.

Characterization of SMG-9, an essential component of the nonsense-mediated mRNA decay SMG1C complex.

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1
Centro de Investigaciones Biológicas, Consejo Superior de Investigaciones Científicas (CSIC), Ramiro de Maetzu 9, 28040 Madrid, Spain.

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.

PMID:
20817927
PMCID:
PMC3017601
DOI:
10.1093/nar/gkq749
[Indexed for MEDLINE]
Free PMC Article
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