Nuclear import of the TATA-binding protein: Mediation by the karyopherin Kap114p and a possible mechanism for intranuclear targeting

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 h ere that nuclear import of TBP is mediated by a new karyopherin (Kap) (impo rtin) family member, Kap114p. Kap114p is localized to the cytoplasm and nuc leus. 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 pat hways for TBP. Consistent with other Kaps, the dissociation of TBP from Kap 114p is dependent on RanGTP. However, we could show that double stranded, T ATA-containing DNA stimulates this RanGTP-mediated dissociation of TBP, and is necessary at lower RanGTP concentrations. This suggests a mechanism whe re, 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 ro le in the intranuclear targeting of TBP.