CHARACTERIZATION OF THE TATA-LESS CORE PROMOTER OF THE CELL-CYCLE-REGULATED CDC25C GENE

The TATA- and inr-less promoter of the human cdc25C gene is regulated during the eel cycle through binding of a repressor to two contiguous promoter-proximal elements, the CDE and CHR. In this study we have cha racterized in detail the region of the cdc25C promoter immediately dow nstream of these elements, Several lines of evidence suggest that this region of -60 bp acts as the core promoter, This sequence: (i) harbor s most of the transcription initiation sites; (ii) possesses basal pro moter activity in vivo; (iii) shows no stable protein binding in vivo as indicated by genomic dimethyl sulfate and phenanthroline copper foo tprinting; (iv) contains single-stranded regions in vivo as shown by p otassium permanganate footprinting; (v) is hypersensitive to DNase I c leavage in permeabilized cells, Mutational analysis of the core promot er revealed the presence of three sites which play a role in transcrip tion, Two of these sites were found to represent low affinity binding sites for transcription factors of the Sp1 family, Mutation of these s ites led to decreased levels of transcription, while their alteration to canonical Sp1 sites impaired cell cycle regulation, Thus the transi ent interaction of Sp1 with the core promoter appears to be necessary for maximal transcription without perturbing cell cycle regulation.