Protein-DNA cross-linking of cultured Drosophila cells has shown that, in vivo, prior to the induction of heat shock, there is approximately one molecule of RNA polymerase II associated with the promoter region of the major heat shock gene, hsp70. Here, we show that this promoter-associated RNA polymerase II molecule is transcriptionally engaged and has formed a nascent RNA chain of approximately 25 nucleotides in length, but is apparently arrested at that point and unable to penetrate further into the hsp70 gene without heat induction. The detection of a post-initiation RNA polymerase complex on the promoter region of the inactive gene suggests that there is a transcriptional control mechanism that acts at a step early in transcript elongation.
Bibliographical noteFunding Information:
We thank our colleagues Mariana Wolfner, Jeffrey Simon, Jeffrey Roberts, and Jay Hirsh for their advise and critical comments regarding this manuscript. We are grateful to Claudia Sutton for initiating the nuclear run-on experiments that led to this work. This work was supported by the National Institutes of Health grant GM 25232 to J. L. and National Research Sevice Award GM 07273 to A. R.