In Vivo Structure of the Cell Cycle-regulated Humancdc25C Promoter

The cdc25C promoter is regulated during the cell cycle by the transcriptional repressor CDF-1 that inhibits the activation function of upstream transcriptional activators, most notably the nuclear factor Y/CAAT box binding factor (NF-Y/CBF). In this report a detailed analysis of the in vivo structure 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 KMnO4footprinting 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 functionally related cyclin A promoter. The structural perturbations seen in DNase I and phenanthroline copper footprints were less pronounced in G0 cells when compared with cycling cells. This presumably reflects a weakened in vivointeraction of NF-Y with its cognate DNA element in G0. It is likely that 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 activation and repression.