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J. Cell Biol.,
Volume 145, Number 7, June 28, 1999 1407-1417
Laboratory of Cell Biology, Howard Hughes Medical Institute, The Rockefeller University, New York 10021
Binding of the TATA-binding protein (TBP)
to the promoter is the first and rate limiting step in the
formation of transcriptional complexes. We show here
that nuclear import of TBP is mediated by a new karyopherin (Kap) (importin) family member, Kap114p. Kap114p is localized to the cytoplasm and nucleus. A
complex of Kap114p and TBP was detected in the cytosol and could be reconstituted using recombinant proteins, suggesting that the interaction was direct. Deletion of the KAP114 gene led to specific mislocalization of TBP to the cytoplasm. We also describe two other
potential minor import pathways for TBP. Consistent
with other Kaps, the dissociation of TBP from Kap114p
is dependent on RanGTP. However, we could show
that double stranded, TATA-containing DNA stimulates this RanGTP-mediated dissociation of TBP, and is
necessary at lower RanGTP concentrations. This suggests a mechanism where, once in the nucleus, TBP is
preferentially released from Kap114p at the promoter
of genes to be transcribed. In this fashion Kap114p may
play a role in the intranuclear targeting of TBP.
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