Plant importin α binds nuclear localization sequences with high affinity and can mediate nuclear import independent of importin β

Stefan Hübner, Harley M S Smith, Wei Hu, Chee Kai Chan, Hans Peter Rihs, Bryce M. Paschal, Natasha V. Raikhel, David A. Jans

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Abstract

Nuclear import of conventional nuclear localization sequence (NLS)- containing proteins initially involves recognition by the importin (IMP) α/β heterodimer, where IMPα binds the NLS and IMPβ targets the IMPα/NLS- containing protein complex to the nuclear pore. Here we examine IMPα from the plant Arabidopsis thaliana (At-IMPα), which exhibits nuclear envelope localization typical of IMPβ rather than IMPα in other eukaryotic cell systems. We show that At-IMPα recognizes conventional NLSs of two different types with high affinity (K(d) of 5-10 nM), in contrast to mouse IMPα (mIMPα), which exhibits much lower affinity (K(d) of 50-70 nM) and only achieves high affinity in the presence of m-IMPβ. Unlike m-IMPα, At-IMPα is thus a high affinity NLS receptor in the absence of IMPβ. Interestingly, At-IMPα was also able to bind with high affinity to NLSs recognized specifically by m-IMPβ and not m-IMPα, including that of the maize transcription factor Opaque-2. Reconstitution of nuclear import in vitro indicated that in the absence of exogenous IMPβ subunit but dependent on RanGDP and NTF2, At-IMPα was able to mediate nuclear accumulation to levels comparable with those mediated by m-IMPα/β. Neither m-IMPα nor -β was able to mediate nuclear import in the absence of the other subunit. At- IMPα's novel NLS recognition and nuclear transport properties imply that plants may possess an IMPα-mediated nuclear import pathway independent of IMPβ in addition to that mediated by IMPα/β.

Original languageEnglish
Pages (from-to)22610-22617
Number of pages8
JournalJournal of Biological Chemistry
Volume274
Issue number32
DOIs
Publication statusPublished - Aug 6 1999
Externally publishedYes

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Karyopherins
Cell Nucleus Active Transport

ASJC Scopus subject areas

  • Biochemistry

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Plant importin α binds nuclear localization sequences with high affinity and can mediate nuclear import independent of importin β. / Hübner, Stefan; Smith, Harley M S; Hu, Wei; Chan, Chee Kai; Rihs, Hans Peter; Paschal, Bryce M.; Raikhel, Natasha V.; Jans, David A.

In: Journal of Biological Chemistry, Vol. 274, No. 32, 06.08.1999, p. 22610-22617.

Research output: Contribution to journalArticle

Hübner, Stefan ; Smith, Harley M S ; Hu, Wei ; Chan, Chee Kai ; Rihs, Hans Peter ; Paschal, Bryce M. ; Raikhel, Natasha V. ; Jans, David A. / Plant importin α binds nuclear localization sequences with high affinity and can mediate nuclear import independent of importin β. In: Journal of Biological Chemistry. 1999 ; Vol. 274, No. 32. pp. 22610-22617.
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AU - Rihs, Hans Peter

AU - Paschal, Bryce M.

AU - Raikhel, Natasha V.

AU - Jans, David A.

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