CONSERVED REGULATORY ELEMENTS IN THE TYPE-I DNA TOPOISOMERASE GENE PROMOTERS OF MOUSE AND MAN

The gene for mammalian type I DNA topoisomerase is constitutively expr essed, but also regulated by a number of external stimuli. We compared the nucleotide sequences of the human and the mouse topoisomerase I g ene promoters because promoter elements, essential for basic as well a s regulated gene expression, should be conserved during evolution. We found that proximal upstream sequences are highly conserved and includ e potential binding sites for ubiquitous transcription factors, a regu latory CRE site as well as two novel promoter elements that have been shown to be important for the expression of the human gene. The more d istal parts of the upstream sequences are less well conserved but incl ude two regions that are almost identical in the human and the mouse g ene. One of these regions contains a binding site for a basic-helix-lo op-helix/leucine-zipper protein, and the other contains an AT-rich ele ment with the potential for DNA bending.