Revealing the
mechanism of HSP104 transcription initiation in the yeast S. cerevisiae.
Melanie R. Grably,
Ariel Stanhill, Osnat Tell, David Engelberg
Dept. of Biological Chemistry, Hebrew University of Jerusalem, Givat Ram,
Jerusalem, 91904, Israel (msgrably@mail.ls.huji.ac.il)
Induction of transcription of stress genes is an accurate process reaching the required level depending on the stress inflicted. In order to understand the mechanisms that underlie this process we analyzed the yeast HSP104 gene promoter. Through 5' deletions, we defined 334bp and 260bp fragments as sufficient and essential for maximal basal activity and heat shock responsiveness respectively. These sequences contain Heat Shock Elements (HSEs) and Stress Response Elements (STREs) that cooperate to achieve maximal inducible expression. However, in the absence of one set of factors (e.g., in msn2Δmsn4Δ cells) full induction is obtained exclusively through HSEs. We also show that HSP104 is constitutively derepressed in ras2Δ cells. This derepression is achieved exclusively through STREs. Further results suggest that HSF is indeed not functional in ras2Δ cells. Strikingly, in ras2Δmsn2Δmsn4Δ cells the HSP104 promoter is also derepressed, but in this strain derepression is mediated through HSEs, suggesting that removal of Msn2/4p re-activate HSF. Collectively, these results show the flexibility and adaptation properties of the promoter. Thus, appropriate transcription of HSP104 is obtained through cooperation between the Msn2/4/STRE and the HSF/HSE systems, but each factor could activate the promoter individually. The study of HSP104 transcription will certainly shed light on transcription regulation under stress in general.