Journal
JOURNAL OF CELL SCIENCE
Volume 117, Issue 17, Pages 3797-3805Publisher
COMPANY BIOLOGISTS LTD
DOI: 10.1242/jcs.01225
Keywords
Drosophila; polytene chromosome; psoralen; supercoil; transcription
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Bulk DNA within the eukaryotic genome is torsionarily relaxed. However, unconstrained negative supercoils of DNA have been detected in few local domains of the genome through preferential binding of psoralen. To make a genome-wide survey for such domains, we introduced biotinylated psoralen into Drosophila salivary glands and visualized it on polytene chromosomes with fluorescent streptavidin. We observed bright psoralen signals on many transcriptionally active interbands and puffs. Upon heat shock, the signals appeared on heat-shock puffs. The signals were resistant to RNase treatment but disappeared or became faint by previous nicking of DNA or inhibition of transcription with cc-amanitin. These data show that transcription-coupled, unconstrained negative supercoils of DNA exist in approximately 150 loci within the interphase genome.
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