NF-Y Histone Fold 1 Helices Help Impart CCAAT Specificity

• Published in: Journal of molecular biology 1999-02, Vol.286 (2), p.327-337
• Main Authors: Zemzoumi, K, Frontini, M, Bellorini, M, Mantovani, R
• Format: Article
• Language: English
• ISSN: 0022-2836
• DOI: 10.1006/jmbi.1998.2496

NF-Y is a conserved trimeric transcriptional activator with an extremely high specificity for CCAAT boxes. The NF-YB and NF-YC subunits have histone fold motifs with a high degree of homology to NC2 alpha / beta , a TBP-binding repressor. The histone fold is composed of three alpha helices, alpha 1, alpha 2, alpha 3, separated by short loops. Structural data on core histones showed that alpha 1 are involved in DNA-binding. To understand the molecular basis of NF-Y sequence-specificity, we constructed deletion and swapping mutants, in which the alpha 1 of NC2 and archeal HMfB, a bona fide histonic protein, was placed in NF-YB and NF-YC. Our analysis indicates that (i) subunit interactions are normal; (ii) NF-YB-NF-YC and NC2 alpha / beta do not form heterodimers and NC2 cannot associate NF-YA. (iii) None of the NF-Y swaps can complex with TBP on a TATA box. (iv) Specific residues, R47 and K49 in NF-YC and N61 in NF-YB, are crucial for CCAAT-binding. We conclude that specificity of the NF-Y trimer is not due to NF-YA only, but stems in part from the contribution of the histone fold alpha 1, particularly that of NF-YB. Copyright 1999 Academic Press