Catabolite control of the elevation of PGK mRNA levels by heat shock in Saccharomyces cerevisiae.

Heat shock enhances the very high level of transcription of the phosphoglycerate kinase (PGK) gene in fermentative cultures of Saccharomyces cerevisiae. This response of PGK mRNA levels was not found on gluconeogenic carbon sources, and could be switched on or off subject to availability of fermentable carbon source. The addition of glucose to yeast growing on glycerol resulted in acquisition, within 30-60 min, of the ability to elevate PGK mRNA levels after heat shock. In addition, in aerobic cultures growing on glucose the exhaustion of the medium glucose coincided with a loss of the heat-shock effect on PGK mRNA and a switch-over to slower growth by aerobic respiration. Levels of hsp26 mRNA were analysed during these experiments. Contrasting with this requirement for fermentable catabolite for manifestation of a heat-shock response of PGK mRNA levels, the PGK enzyme was not synthesized at a greater level in heat-shocked fermentative than in gluconeogenic cultures. PGK is one of only a few proteins made efficiently after mild heat shock of yeast. Thus, heat-stress-induced elevation of PGK mRNA levels does not appreciably increase PGK synthesis during exposure to high temperatures and so its role may be to assist cells repressed in mitochondrial function during recovery following a heat shock.