Hypoxia abolishes transience of the heat-shock response in the methylotrophic yeast Hansenula polymorpha.
The heat-shock response is conserved amongst practically all organisms. Almost invariably, the massive heat-shock protein (Hsp) synthesis that it induces is subsequently down-regulated, making this a transient, not a sustained, stress response. This study investigated whether the heat-shock response displays any unusual features in the methylotrophic yeast Hansenula polymorpha, since this organism exhibits the highest growth temperature (49-50 degrees C) identified to date for any yeast and grows at 47 degrees C without either thermal death or detriment to final biomass yield. Maximal levels of Hsp induction were observed with a temperature upshift of H. polymorpha from 30 degrees C to 47-49 degrees C. This heat shock induces a prolonged growth arrest, heat-shock protein synthesis being down-regulated long before growth resumes at such high temperatures. A 30 degrees C to 49 degrees C heat shock also induced thermotolerance, although H. polymorpha cells in balanced growth at 49 degrees C were intrinsically thermotolerant. Unexpectedly, the normal transience of the H. polymorpha heat-shock response was suppressed completely by imposing the additional stress of hypoxia at the time of the 30 degrees C to 49 degrees C temperature upshift. Hypoxia abolishing the transience of the heat-shock response appears to operate at the level of Hsp gene transcription, since the heat-induced Hsp70 mRNA was transiently induced in a heat-shocked normoxic culture but displayed sustained induction in a culture deprived of oxygen at the time of temperature upshift.
Guerra
Emanuela
E
Laboratorio di Genetica Microbica, DiSA, Università Politecnica delle Marche, 60131 Ancona, Italy.
Chye
Poh Poh
PP
Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield, S10 2TN, UK.
Berardi
Enrico
E
Laboratorio di Genetica Microbica, DiSA, Università Politecnica delle Marche, 60131 Ancona, Italy.
Piper
Peter W
PW
Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield, S10 2TN, UK.
D002453:Cell Cycle / Q000187:drug effects; D015966:Gene Expression Regulation, Fungal; D018840:HSP70 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D006360:Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism; D018869:Heat-Shock Response / Q000187:drug effects*; D006358:Hot Temperature; D010100:Oxygen / Q000494:pharmacology*; D010843:Pichia / Q000187:drug effects / Q000254:growth & development* / Q000502:physiology; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D013696:Temperature
D018840:HSP70 Heat-Shock Proteins; D006360:Heat-Shock Proteins; D012333:RNA, Messenger; D010100:Oxygen