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Snurportin1, an m 3 G‐cap‐specific nuclear import receptor with a novel domain structure
Author(s) -
Huber Jochen,
Cronshagen Udo,
Kadokura Michinori,
Marshallsay Christopher,
Wada Takeshi,
Sekine Mitsuo,
Lührmann Reinhard
Publication year - 1998
Publication title -
the embo journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 7.484
H-Index - 392
eISSN - 1460-2075
pISSN - 0261-4189
DOI - 10.1093/emboj/17.14.4114
Subject(s) - snrnp , biology , importin , nuclear transport , karyopherin , microbiology and biotechnology , nuclear localization sequence , nls , cell nucleus , biochemistry , ribonucleoprotein , rna , gene , nucleus , cytoplasm
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 (m 3 G) 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 m 3 G‐cap but not m 7 G‐cap structures. Snurportin1 enhances the m 3 G‐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 m 3 G‐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 β binding (IBB) domain, essential for function, and a C‐terminal m 3 G‐cap‐binding region with no structural similarity to the arm repeat domain of importin α.