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. 2007 Mar 16;282(11):7799-808.
doi: 10.1074/jbc.M610159200. Epub 2007 Jan 17.

Distant N- and C-terminal domains are required for intrinsic kinase activity of SMG-1, a critical component of nonsense-mediated mRNA decay

Tomoko Morita  1 , Akio Yamashita, Isao Kashima, Kazuhiro Ogata, Shoichi Ishiura, Shigeo Ohno
Affiliations
Free article

Distant N- and C-terminal domains are required for intrinsic kinase activity of SMG-1, a critical component of nonsense-mediated mRNA decay

Tomoko Morita et al. J Biol Chem. .
Free article

Abstract

Phosphatidylinositol 3-kinase-related kinases (PIKKs) consisting of SMG-1, ATM, ATR, DNA-PKcs, and mTOR are a family of proteins involved in the surveillance of gene expression in eukaryotic cells. They are involved in mechanisms responsible for genome stability, mRNA quality, and translation. They share a large N-terminal domain and a C-terminal FATC domain in addition to the unique serine/threonine protein kinase (PIKK) domain that is different from classical protein kinases. However, structure-function relationships of PIKKs remain unclear. Here we have focused on one of the PIKK members, SMG-1, which is involved in RNA surveillance, termed nonsense-mediated mRNA decay (NMD), to analyze the roles of conserved and SMG-1-specific sequences on the intrinsic kinase activity. Analyses of sets of point and deletion mutants of SMG-1 in a purified system and intact cells revealed that the long N-terminal region and the conserved leucine in the FATC domain were essential for SMG-1 kinase activity. However, the conserved tryptophan in the TOR SMG-1 (TS) homology domain and the FATC domain was not. In addition, the long insertion region between PIKK and FATC domains was not essential for SMG-1 kinase activity. These results indicated an unexpected feature of SMG-1, i.e. that distantly located N- and C-terminal sequences were essential for the intrinsic kinase activity.

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