The heat shock response in yeast: differential regulations and contributions of the Msn2p/Msn4p and Hsf1p regulons

The heat shock transcription factor Hsf1p and the stress-responsive transcr iption factors Msn2p and Msn4p are activated by heat shock in the yeast Sac charomyces cerevisiae. Their respective contributions to heat shock protein induction have been analysed by comparison of mutants and wild-type strain s using [S-35]-methionine labelling and two-dimensional gel electrophoresis . Among 52 proteins induced by a shift from 25 degrees C to 38 degrees C, h alf of them were found to be dependent upon Msn2p and/or Msn4p (including m ostly antioxidants and enzymes involved in carbon metabolism), while the ot her half (including mostly chaperones and associated proteins) were depende nt upon Hsf1p. The two sets of proteins overlapped only slightly. Three pro teins were induced independently of these transcription factors, suggesting the involvement of other transcription factor(s). The Ras/cAMP/PKA signall ing pathway cAMP had a negative effect on the induction of the Msn2p/Msn4p regulon, but did not affect the Hsf1p regulon, Thus, the two types of trans cription factor are regulated differently and control two sets of functiona lly distinct proteins, suggesting two different physiological roles in the heat shock cellular response.