Modulation of heat shock gene expression by the TAC1 chromatin-modifying complex

Abstract

Rapid induction of the Drosophila melanogaster heat shock gene hsp70 is achieved through the binding of heat shock factor¹ (HSF) to heat shock elements (HSEs) located upstream of the transcription start site² (reviewed in ref. 3). The subsequent recruitment of several other factors^4,5,6,7,8, including Spt5, Spt6 and FACT, is believed to facilitate Pol II elongation through nucleosomes downstream of the start site^9,10,11. Here, we report a novel mechanism of heat shock gene regulation that involves modifications of nucleosomes by the TAC1 histone modification complex¹². After heat stress, TAC1 is recruited to several heat shock gene loci, where its components are required for high levels of gene expression. Recruitment of TAC1 to the 5′-coding region of hsp70 seems to involve the elongating Pol II complex. TAC1 has both histone H3 Lys 4-specific (H3-K4) methyltransferase (HMTase) activity and histone acetyltransferase activity through Trithorax (Trx) and CREB-binding protein (CBP), respectively. Consistently, TAC1 is required for methylation and acetylation of nucleosomal histones in the 5′-coding region of hsp70 after induction, suggesting an unexpected role for TAC1 during transcriptional elongation.