PMID:15964792

Citation	Kahle, J, Baake, M, Doenecke, D and Albig, W (2005) Subunits of the heterotrimeric transcription factor NF-Y are imported into the nucleus by distinct pathways involving importin beta and importin 13. Mol. Cell. Biol. 25:5339-54
Abstract	The transcriptional activator NF-Y is a heterotrimeric complex composed of NF-YA, NF-YB, and NF-YC, which specifically binds the CCAAT consensus present in about 30% of eukaryotic promoters. All three subunits contain evolutionarily conserved core regions, which comprise a histone fold motif (HFM) in the case of NF-YB and NF-YC. Our results of in vitro binding studies and nuclear import assays reveal two different transport mechanisms for NF-Y subunits. While NF-YA is imported by an importin beta-mediated pathway, the NF-YB/NF-YC heterodimer is translocated into the nucleus in an importin 13-dependent manner. We define a nonclassical nuclear localization signal (ncNLS) in NF-YA, and mutational analysis indicates that positively charged amino acid residues in the ncNLS are required for nuclear targeting of NF-YA. Importin beta binding is restricted to the monomeric, uncomplexed NF-YA subunit. In contrast, the nuclear import of NF-YB and NF-YC requires dimer formation. Only the NF-YB/NF-YC dimer, but not the monomeric components, are recognized by importin 13 and are imported into the nucleus. Importin 13 competes with NF-YA for binding to the NF-YB/NF-YC dimer. Our data suggest that a distinct binding platform derived from the HFM of both subunits, NF-YB/NF-YC, mediates those interactions.
Links	PubMed PMC1157003 Online version:10.1128/MCB.25.13.5339-5354.2005
Keywords	Amino Acid Motifs; Amino Acid Sequence; Animals; Binding, Competitive; CCAAT-Binding Factor/chemistry; CCAAT-Binding Factor/genetics; CCAAT-Binding Factor/isolation & purification; CCAAT-Binding Factor/metabolism; Cell Nucleus/metabolism; Conserved Sequence; Dimerization; Female; Glutathione Transferase/metabolism; HeLa Cells; Humans; Karyopherins/metabolism; Microinjections; Molecular Sequence Data; Mutagenesis, Site-Directed; Oocytes; Protein Binding; Protein Subunits/chemistry; Protein Subunits/metabolism; Recombinant Fusion Proteins/chemistry; Recombinant Fusion Proteins/isolation & purification; Recombinant Fusion Proteins/metabolism; Sequence Homology, Amino Acid; Xenopus laevis; beta Karyopherins/metabolism
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