Structural characterization of the human DNA topoisomerase I gene promoter

Abstract

We have isolated a genomic DNA fragment from HeLa cells containing the promoter region and the first two exons of the human gene encoding DNA topoisomerase I (hTOP1). Transcription of hTOP1 mRNA initiates at multiple sites which are clustered 247 nucleotides and 210 nucleotides upstream of the translation‐initiation site of the protein coding region. The nucleotide sequence of the region preceding the transcription‐initiation sites is G/C rich and contains sequence motifs which are known binding sites of the transcription factors Oct1 (octameric transcription factor 1), Sp1 and AP2 (activator protein 2). Furthermore, one cAMP‐responsive element is present 50 nucleotides upstream of the transcription‐initiation site nearest the 5′ end. Neither TATA nor CAAT boxes were found in the promoter region of the hTOP1 gene. A 918‐bp fragment containing the sequence elements described above drives the transient expression of a chloramphenicol acetyl transferase (CAT) gene sequence in transfected HeLa and 293 cells. In addition we analyzed a 10‐kb fragment containing the promoter and exons 1 and 2 for regions of DNase I hypersensitivity. We detected one prominent DNase‐I‐hypersensitive region in the promoter close to the putative transcription‐factor‐binding sites and several weaker regions in intron 2. Copyright © 1990, Wiley Blackwell. All rights reserved