RNAi screen in Drosophila larvae identifies histone deacetylase 3 as a positive regulator of the hsp70 heat shock gene expression during heat shock

• We describe a screen for identifying proteins that affect hsp70 transcription.
• We identify HDAC3 and SMRTER as positive regulators of hsp70 expression.
• HDAC3 regulates hsp70 expression at step subsequent to activation of the paused Pol II by HSF.

The transcription regulation of the Drosophila hsp70 gene is a complex process that involves the regulation of multiple steps, including the establishment of paused Pol II and release of Pol II into elongation upon heat shock activation. While the major players involved in the regulation of gene expression have been studied in detail, additional factors involved in this process continue to be discovered. To identify factors involved in hsp70 expression, we developed a screen that capitalizes on a visual assessment of heat shock activation using a hsp70-beta galactosidase reporter and publicly available RNAi fly lines to deplete candidate proteins. We validated the screen by showing that the depletion of HSF, CycT, Cdk9, Nurf 301, or ELL prevented the full induction of hsp70 by heat shock. Our screen also identified the histone deacetylase HDAC3 and its associated protein SMRTER as positive regulators of hsp70 activation. Additionally, we show that HDAC3 and SMRTER contribute to hsp70 gene expression at a step subsequent to HSF-mediated activation and release of the paused Pol II that resides at the promoter prior to heat shock induction.