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. 1998 Jul 15;17(14):4114–4126. doi: 10.1093/emboj/17.14.4114

Snurportin1, an m3G-cap-specific nuclear import receptor with a novel domain structure.

J Huber 1, U Cronshagen 1, M Kadokura 1, C Marshallsay 1, T Wada 1, M Sekine 1, R Lührmann 1
PMCID: PMC1170744  PMID: 9670026

Abstract

The nuclear import of the spliceosomal snRNPs U1, U2, U4 and U5, is dependent on the presence of a complex nuclear localization signal (NLS). The latter is composed of the 5'-2,2,7-terminal trimethylguanosine (m3G) cap structure of the U snRNA and the Sm core domain. Here, we describe the isolation and cDNA cloning of a 45 kDa protein, termed snurportin1, which interacts specifically with m3G-cap but not m7G-cap structures. Snurportin1 enhances the m3G-capdependent nuclear import of U snRNPs in both Xenopus laevis oocytes and digitonin-permeabilized HeLa cells, demonstrating that it functions as an snRNP-specific nuclear import receptor. Interestingly, solely the m3G-cap and not the Sm core NLS appears to be recognized by snurportin1, indicating that at least two distinct import receptors interact with the complex snRNP NLS. Snurportin1 represents a novel nuclear import receptor which contains an N-terminal importin beta binding (IBB) domain, essential for function, and a C-terminal m3G-cap-binding region with no structural similarity to the arm repeat domain of importin alpha.

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Selected References

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