Disruption of downstream chromatin directed by a transcriptional activator.

Promoter-proximal pausing during transcriptional elongation is an important way of regulating many diverse loci, including the human hsp70 gene. Pausing of RNA polymerase can be enhanced by chromatin structure. We demonstrate that activation of hsp70 leads to disruption of transcribed chromatin in front of RNA polymerase. In vivo, disruption of chromatin in the first 400 bp of the transcribed region of hsp70 following heat shock is resistant to the transcriptional inhibitor alpha-amanitin. Disruption of chromatin farther downstream also occurs following activation but is sensitive to alpha-amanitin, suggesting that polymerase movement is needed to disrupt distal portions of the hsp70 gene. In vitro, disruption of transcribed chromatin is dependent on the presence of the human heat shock factor 1 (HSF1) activation domains. These experiments demonstrate that HSF1 can direct disruption of chromatin in transcribed regions. We suggest that this is one of the mechanisms used by HSF1 to facilitate transcriptional elongation.