Dissection of the NF-Y transcriptional activation potential

NF-Y is a trimeric CCAAT-binding factor with histone fold subunits (NF-YB/N F-YC) and bipartite activation domains located on NF-YA and NF-YC, We recon stituted the NF-Y activation potential in vivo with GAL4 DBD fusions, In th e GAL4-YA configuration, activation requires co-expression of the three sub units; with GAL4-YB and GAL4-YC, transfections of the histone fold partners are sufficient, provided that the Q-rich domain of NF-YC is present, Combi nations of mutants indicate that the Q-rich domains of NF-YA and NF-YC are redundant in the trimeric complex, Glutamines 101 and 102 of NF-YA are requ ired for activity, We assayed NF-Y on different promoter targets, containin g single or multiple GAL4 sites: whereas on a single site NF-Y is nearly as powerful as VP16, on multiple sites neither synergistic nor additive effec ts are observed, NF-Y activates TATA and Inr core elements and the overall potency is in the same range as other Q-rich and Pro-rich activation domain s. These results represent the first in vivo evidence of subunit interactio ns studies and further support the hypothesis that NF-Y is a general promot er organizer rather than a brute activator.