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Molecular and Cellular Biology, May 2005, p. 3543-3552, Vol. 25, No. 9
0270-7306/05/$08.00+0 doi:10.1128/MCB.25.9.3543-3552.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.
Center for Gene Regulation, Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania
Received 9 January 2005/ Accepted 19 January 2005
We analyzed the impact of a GAGA element on a transgenic promoter in Drosophila melanogaster that was activated by proteins composed of the Teton DNA binding domain and either the heat shock factor (HSF) activation domain or a potent subdomain of VP16. Permanganate footprinting was used to monitor polymerase II (Pol II) on the transgenic promoters in vivo. Activation by Teton-HSF but not by Teton-VP16A2 required the GAGA element; this correlated with the ability of the GAGA element to establish a paused Pol II. Although the GAGA element was not required for activation by Teton-VP16A2, the GAGA element greatly accelerated the rate of activation. The permanganate data also provided evidence that Pol II encountered different rate-limiting steps, following initiation in the presence of Teton-HSF and Teton-VP16A2. The rate-limiting step in the presence of Teton-HSF was release of Pol II paused about 20 to 40 nucleotides downstream from the start site. The rate-limiting step in the presence of Teton-VP16A2 occurred much closer to the transcription start site. Several biochemical studies have provided evidence for a structural transition shortly after Pol II initiates transcription. The behavior of Pol II in the presence of Teton-VP16A2 provides the first evidence that this transition occurs in vivo.
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