SMG-8 and SMG-9, two novel subunits of the SMG-1 complex, regulate remodeling of the mRNA surveillance complex during nonsense-mediated mRNA decay

Akio Yamashita; Natsuko Izumi; Isao Kashima; Tetsuo Ohnishi; Bonnie Saari; Yukiko Katsuhata; Reiko Muramatsu; Tomoko Morita; Akihiro Iwamatsu; Takahisa Hachiya; Rie Kurata; Hisashi Hirano; Philip Anderson; Shigeo Ohno

doi:10.1101/gad.1767209

SMG-8 and SMG-9, two novel subunits of the SMG-1 complex, regulate remodeling of the mRNA surveillance complex during nonsense-mediated mRNA decay

¹Department of Molecular Biology, Yokohama City University School of Medicine, Yokohama 236-0004, Japan;
²Precursory Research for Embryonic Science and Technology (PRESTO), Japan Science and Technology Agency, Kawaguchi 332-0012, Japan;
³Department of Genetics, University of Wisconsin at Madison, Madison, Wisconsin 53706, USA;
⁴Department of Obstetrics and Gynecology, Yokohama City University School of Medicine, Yokohama 236-0004, Japan;
⁵Protein Research Network Co. Ltd., Yokohama 236-0004, Japan;
⁶Ina Laboratory, Medical and Biological Laboratories Co. Ltd., Ina 396-0022, Japan;
⁷International Graduate School of Arts and Sciences, Yokohama City University, Yokohama 230-0045, Japan

8
↵8 These authors contributed equally to this work.

Abstract

Nonsense-mediated mRNA decay (NMD) is a surveillance mechanism that detects and degrades mRNAs containing premature translation termination codons (PTCs). SMG-1 and Upf1 transiently form a surveillance complex termed “SURF” that includes eRF1 and eRF3 on post-spliced mRNAs during recognition of PTC. If an exon junction complex (EJC) exists downstream from the SURF complex, SMG-1 phosphorylates Upf1, the step that is a rate-limiting for NMD. We provide evidence of an association between the SURF complex and the ribosome in association with mRNPs, and we suggest that the SURF complex functions as a translation termination complex during NMD. We identified SMG-8 and SMG-9 as novel subunits of the SMG-1 complex. SMG-8 and SMG-9 suppress SMG-1 kinase activity in the isolated SMG-1 complex and are involved in NMD in both mammals and nematodes. SMG-8 recruits SMG-1 to the mRNA surveillance complex, and inactivation of SMG-8 induces accumulation of a ribosome:Upf1:eRF1:eRF3:EJC complex on mRNP, which physically bridges the ribosome and EJC through eRF1, eRF3, and Upf1. These results not only reveal the regulatory mechanism of SMG-1 kinase but also reveal the sequential remodeling of the ribosome:SURF complex to the predicted DECID (DECay InDucing) complex, a ribosome:SURF:EJC complex, as a mechanism of in vivo PTC discrimination.

Keywords

Footnotes

9
↵9 Present addresses: Max-Planck-Institute for Developmental Biology, D-72076 Tübingen, Germany
10
↵10 Laboratory for Molecular Psychiatry, Brain Science Institute, RIKEN, Wako 351-0198, Japan.
11
↵11 Corresponding authors.

↵E-MAIL ohnos{at}med.yokohama-cu.ac.jp; FAX 81-45-785-4140.
12
↵12 E-MAIL yamasita{at}yokohama-cu.ac.jp; FAX 81-45-785-4140.
Article is online at http://www.genesdev.org/cgi/doi/10.1101/gad.1767209.
Supplemental material is available at http://www.genesdev.org.
- Received November 25, 2008.
- Accepted March 23, 2009.