The unfolded protein response transducer Ire1p contains a nuclear localization sequence recognized by multiple beta importins

Department of Biochemistry and Molecular Biology, University of Melbourne, Victoria 3010, Australia.
Molecular Biology of the Cell (Impact Factor: 4.47). 01/2007; 17(12):5309-23. DOI: 10.1091/mbc.E06-04-0292
Source: PubMed


The Ire1p transmembrane receptor kinase/endonuclease transduces the unfolded protein response (UPR) from the endoplasmic reticulum (ER) to the nucleus in Saccharomyces cerevisiae. In this study, we analyzed the capacity of a highly basic sequence in the linker region of Ire1p to function as a nuclear localization sequence (NLS) both in vivo and in vitro. This 18-residue sequence is capable of targeting green fluorescent protein to the nucleus of yeast cells in a process requiring proteins involved in the Ran GTPase cycle that facilitates nuclear import. Mutagenic analysis and importin binding studies demonstrate that the Ire1p linker region contains overlapping potential NLSs: at least one classical NLS (within sequences 642KKKRKR647 and/or 653KKGR656) that is recognized by yeast importin alpha (Kap60p) and a novel betaNLS (646KRGSRGGKKGRK657) that is recognized by several yeast importin beta homologues. Kinetic binding data suggest that binding to importin beta proteins would predominate in vivo. The UPR, and in particular ER stress-induced HAC1 mRNA splicing, is inhibited by point mutations in the Ire1p NLS that inhibit nuclear localization and also requires functional RanGAP and Ran GEF proteins. The NLS-dependent nuclear localization of Ire1p would thus seem to be central to its role in UPR signaling.

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Available from: Edouard Nice
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    • "Conventional splicing takes place exclusively in the nucleus, but it has been controversial where the splicing reaction of unconventional splicing occurs (see Discussion). Unconventional splicing of yeast HAC1 mRNA is thought to occur in the cytoplasm (Ruegsegger et al., 2001), although Gething and colleagues argued that it occurs in the nucleus as well as cytoplasm (Goffin et al., 2006). Regarding mammalian unconventional splicing, it was reported that IRE1 is localized in the inner nuclear membrane, suggesting that it takes place in the nucleus (Lee et al., 2002). "
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    • "Their nuclear import is directed by a NLS and is also dependent on the function of nuclear pore complex–associated proteins (Nups). Ire1p, a regulator of the unfolded protein response and previously thought be an ER membrane protein, has been shown to contain a NLS and preferentially localize to the INM (Goffin et al., 2006). In contrast, like Doa10p, Zmp- ste24 and Icmt contain no obvious NLS as predicted by the PSORT II algorithm and do not concentrate in the INM, yet they also reside and are active within the nucleus, as shown here. "
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