THE PROMOTER REGION OF THE HUMAN TYPE-I-DNA-TOPOISOMERASE GENE - PROTEIN-BINDING SITES AND SEQUENCES INVOLVED IN TRANSCRIPTIONAL REGULATION

We examined the promoter of the human type-I-DNA topoisomerase gene (h TOP1) for regions protected against DNase I digestion by nuclear prote ins from HeLa or from adenovirus-transformed 293 cells. We identified ten protected DNA sequences within 580 bp of DNA upstream of the trans criptional-start sites and one additional site, which is located betwe en the two clusters of transcriptional-start sites. Several of these p rotein-binding sites have significant similarities to recognition sequ ences of known transcription factors including factors Sp1, octamer tr anscription factor, cAMP-responsive-element-binding protein (CREB/ATF) , NF-kappaB and members of the Myc-related family of basic/helix-loop- helix/leucine-zipper proteins. Other protein-binding sites show less o r no similarities to known consensus sequences. We investigated the ph ysiological significance of these protein-binding sites using a set of deletion and nucleotide-exchange mutants. We conclude that the expres sion of the hTOP1 gene is regulated by a complex network of negatively and positively acting transcription factors.