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© The Rockefeller University Press, 0021-9525/1999//235 $5.00
The Journal of Cell Biology, Volume 147, Number 2, , 1999 235-246

Original Article

The Karyopherin Kap122p/Pdr6p Imports Both Subunits of the Transcription Factor Iia into the Nucleus



Anton A. Titova and Günter Blobela

a Laboratory of Cell Biology, Howard Hughes Medical Institute, The Rockefeller University, New York, New York 10021
Laboratory of Cell Biology, Howard Hughes Medical Institute, The Rockefeller University, 1230 York Avenue, New York, NY 10021.(212) 327-7880(212) 327-8096

blobel{at}rockvax.rockefeller.edu

We discovered a nuclear import pathway mediated by the product of the previously identified Saccharomyces cerevisiae gene PDR6 (pleiotropic drug resistance). This gene product functions as a karyopherin (Kap) for nuclear import. Consistent with previously proposed nomenclature, we have renamed this gene KAP122. Kap122p was localized both to the cytoplasm and the nucleus. As a prominent import substrate of Kap122p, we identified the complex of the large and small subunit (Toa1p and Toa2p, respectively) of the general transcription factor IIA (TFIIA). Recombinant GST-Kap122p formed a complex with recombinant His6-Toa1p/Toa2p. In wild-type cells, Toa1p and Toa2p were localized to the nucleus. Consistent with Kap122p being the principal Kap for import of the Toa1p–Toa2p complex, we found that deletion of KAP122 results in increased cytoplasmic localization of both Toa1p and Toa2p. Deletion of KAP122 is not lethal, although deletion of TOA1 and TOA2 is. Together these data suggest that Kap122p is the major Kap for the import of Toa1p–Toa2p into the nucleus. Like other substrate–Kap complexes, the Toa1p/Toa2p/Kap122p complex isolated from yeast cytosol or reconstituted from recombinant proteins, was dissociated by RanGTP but not RanGDP. Kap122p bound to nucleoporins, specifically, to the peptide repeat–containing fragments of Nup1p and Nup2p.

Key Words: yeast • karyopherin β family • nuclear import • transcription factor IIA • RanGTP dissociation

© 1999 The Rockefeller University Press

1.used in this paper: DAPI, 4',6-diamidino-2-phenylindole; Kap, karyopherin; NLS, nuclear localization signal; NPC, nuclear pore complex; Nup, nucleoporin; PDR6, pleiotropic drug resistance; PrA, Staphylococcus aureus protein A; TBP, TATA-binding protein; TFIIA, transcription factor IIA


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