Nucleic Acids Research, 1989, Vol. 17, No. 21 8495-8509
© 1989
ENZYMOLOGY |
Interaction of topoisomerase 1 with the transcribed region of the Drosophila HSP 70 heat shock gene
Department of Pharmacology and Therapeutics, University of Florida College of Medicine Gainesville, FL 32610, USA
*To whom correspondence should be addressed
Received August 4, 1989. Revised October 4, 1989. Accepted October 4, 1989.
Topoisomerase I cleavage sites have been mapped in vivo on the Hsp70 heat shock gene of Drosophila melanogaster cells using the drug camptothecin. Topoisomerase I cleavage was only observed when the Hsp70 gene was transcriptionally active. Site-specific single-strand DNA cleavage by topoisomerase I was confined to the transcribed region of the Hsp70 gene and occurred on both the transcribed and nontranscribed DNA strands. A number of the single-strand breaks on the complementary DNA strands occurred in close proximity giving rise to double-stranded DNA breaks. Inhibition of heat-induced Hsp70 transcription by either Actinomycin D (Act D) or 5,6-dichloro-1-ß-D-ribofuranosylbenzimidazole (DRB) inhibited topoisomerase I cleavage except at the 5' and to a lesser extent the 3' end of the gene. Camptothecin (100 µM) inhibited transcription of the Hsp70 gene greater than 95%. These results suggest that topoisomerase I is intimately associated with and has an integral part in Hsp70 gene transcription.
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