A heat shock element in the phosphoglycerate kinase gene promoter of yeast

The phosphoglycerate kinase (PGK) promoter is often employed in yeast expression vectors due to its very high efficiency. Its activity in un-stressed cells has been shown to be due to an upstream activator site (UAS p™) at-402 to-479. Since levels of PGK mRNA can sometimes be elevated by heif shock of yeast cultures this investigation determined how specific deletions of PGK promoter sequences affect levels of PGK mRNA both before and after heat shock. A series of PGK promoter deletions vas inserted on a high copy plasmid into cells having a TRP1 gene disruption of the solitary chromosomal PGK locus. This enabled PGK transcripts of plasmid and chromosomal origin to be distinguished by virtue of their different sizes. Certain deletions lacking UAS displayed activities that were very low in unstressed cells, but which increased fifty to one-hundred fold after heat shock. With UAS present heat shock had only a relatively small or negligible effect on PGK mRNA levels. Heat shock activation was abolished when the-256 to-377 region with homology to the heat shock element consensus of eukaryotes was deleted in addition to UAS, but was unaffected by the deletion of regions further downstream containing TATA- and CAAT- sequence motifs. This is the first demonstration of a heat shock element, an activator site normally found up-stream of eukaryotic heat shock protein genes, as a natural constituent of a high efficiency glycolytic promoter. It is proposed that PGK may be one member of a small subset of yeast genes that are highly expressed in unstressed cells yet possess a heat shock element to ensure their continued transcription after heat shock