Transcription of the major Drosophila heat-shock gene in vitro

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Abstract
Active eukaryotic genes are more accessible to some proteins that bind DNA than are inactive genes. To probe the accessibility of the Drosophila heat-shock genes, isolated nuclei from Drosophila tissue culture cells were used as templates for Escherichia coli RNA polymerase. With nuclei isolated from cells that were not heat shocked, the synthesis of heat-shock RNA was not detected by hybridization to a DNA clone containing sequences from the major heat-shock region. Approximately 0.22% of the RNA synthesized in nuclei isolated from cells that were previously heat shocked hybridized to the heat-shock clone. The synthesis of heat-shock RNA was DNA dependent, was sensitive to rifampicin and to actinomycin D and represented a 70-fold enrichment over random transcription of the Drosophila genome. Transcription showed an extraordinary preference for a region 5'' distal to the structural gene. Preferential transcription by the bacterial RNA polymerase is indicative of the active state of Drosophila genes.