title: Topoisomerase I interacts with transcribed regions in Drosophila cells.
abstract: The in vivo distribution of topoisomerase I on specific DNA sequences is determined at high resolution in Drosophila cells using a photo-crosslinking method. Topoisomerase I-DNA adducts are generated by irradiation of intact cells with UV light and then purified by immunoprecipitation with antibody to topoisomerase I. Analyses of the DNA sequences crosslinked to topoisomerase I by blot-hybridization with appropriate DNA probes indicate that topoisomerase I is concentrated on transcribed regions and not on nontranscribed flanking sequences. Like RNA polymerase II, topoisomerase I is recruited to heat-shock genes during the heat-shock response. However, topoisomerase I and RNA polymerase II can interact independently with the transcribed region because different ratios of topoisomerase I and RNA polymerase II are crosslinked to the highly transcribed hsp70 gene and the moderately transcribed copia genes. We hypothesize that topoisomerase I allows topological changes in DNA that are required for transcription.
mesh_terms: D000818:Animals; D001483:Base Sequence; D002478:Cells, Cultured; D004247:DNA / Q000235:genetics / Q000378:metabolism*; D004264:DNA Topoisomerases, Type I / Q000378:metabolism*; D004330:Drosophila; D005796:Genes; D006360:Heat-Shock Proteins / Q000235:genetics; D006358:Hot Temperature; D009693:Nucleic Acid Hybridization; D012319:RNA Polymerase II / Q000378:metabolism; D014158:Transcription, Genetic
chemical_list: D006360:Heat-Shock Proteins; D004247:DNA; D012319:RNA Polymerase II; D004264:DNA Topoisomerases, Type I