NF-Y-dependent regulation of chromatin structure on cell cycle promoters

NF-Y is an ubiquitous trascription factor comprising three subunits, NF-YA, NF-YB, and NF-YC. NF-YB and NF-YC, H2A/H2B like, contain histone fold motifs (HFM), found in all core histones, whose dimerization is a prerequisite for NF-YA association, that confers to the trimer CCAAT-specific DNA binding capacity. NF-Y binding is a prerequisite for promoter activation, as it pre-sets the promoter architecture in the near proximity of transcriptional start site allowing other regulatory proteins to access it. ChIP experiments determined that NF-Y binding to cell-cycle genes occurs in vivo before gene activation and in a very strictly regulated manner. To investigate the role of NF-Y in the regulation of chromatin structure on cell cycle promoters, we performed ChIP analysis on cycling, G2/M blocked and G1 synchronized HCT116 cells, by using chromatin micrococcal digested. From a fine nucleosome mapping of human CyclinB2 (marker of G2/M phase) and PCNA (G1 phase) we found a complementary pattern of expression between NF-Y subunits and core histones: far from the trascriptional start site enrichment is greater in core histones than in NF-Y subunits, while getting closer to the trascriptional start site the situation is reversed. Predictably, this is observed in G2/M blocked cells on CyclinB2 promoter, whereas on the PCNA promoter occurs in G1 synchronized cells. At the opposite, we observed H2A/H2B on CyclinB2 core promoter in G1 cells and on PCNA in G2/M cells. H3/H4 behaves differently from H2A/H2B, as they are enriched either on the core promoter or far from it. We conclude that NF-Y acts not only as a classical trascription factor, but it also has a crucial role in nucleosomes remodelling within active chromatin.