The cdc25C promoter is regulated during the cell cycle by the transcription
al repressor CDF-1 that inhibits the activation function of upstream transc
riptional activators, most notably the nuclear factor Y/CAAT box binding fa
ctor (NF-Y/CBF), In this report a detailed analysis of the in vivo structur
e of the cdc25C promoter was made. Micrococcus nuclease and methidiumpropyl
-EDTA footprinting strongly suggest that the proximal promoter encompassing
the cell cycle-dependent element/cell cycle genes homology region and the
upstream NF-Y sites is organized in a positioned nucleosome throughout the
cell cycle. Furthermore, structural perturbations were detected by DNase I,
phenanthroline copper, and KMnO4 footprinting at the NF-Y binding sites in
vivo, which is in agreement with the reported property of NF-Y to bend DNA
in vitro. Similar results were obtained with the structurally and function
ally related cyclin A promoter. The structural perturbations seen in DNase
I and phenanthroline copper footprints were less pronounced in G(0) cells w
hen compared with cycling cells. This presumably reflects a weakened in viv
o interaction of NF-Y with its cognate DNA element in G(0). It is likely th
at these structural perturbations, together with the reported ability of NF
-Y to recruit histone acetyl transferase activity, contribute to an opened
chromatin structure as a prerequisite for optimal regulation through activa
tion and repression.