Transcriptional regulation of an hsp70 heat shock gene in the yeast Saccharomyces cerevisiae.

The yeast Saccharomyces cerevisiae contains three heat-inducible hsp70 genes. We have characterized the promoter region of the hsp70 heat shock gene YG100, that also displays a basal level of expression. Deletion of the distal region of the promoter resulted in an 80% drop in the basal level of expression without affecting expression after heat shock. Progressive-deletion analysis suggested that sequences necessary for heat-inducible expression are more proximal, within 233 base pairs of the initiation region. The promoter region of YG100 contains multiple elements related to the Drosophila melanogaster heat shock element (HSE; CnnGAAnnT TCnnG). Deletion of a proximal promoter region containing one element, HSE2, eliminated most of the heat-inducible expression of YG100. The upstream activation site (UAS) of the yeast cytochrome c gene (CYC1) can be substituted by a single copy of HSE2 plus its adjoining nucleotides (UASHS). This hybrid promoter displayed a substantial level of expression before heat shock, and the level of expression was elevated eightfold by heat shock. YG100 sequences that flank UASHS inhibited basal expression of UASHS in the hybrid promoter but not its heat-inducible expression. This inhibition of basal UASHS activity suggests that negative regulation is involved in modulating expression of this yeast heat shock gene.     

Protein/DNA architecture of the DNase I hypersensitive region of the Drosophila hsp26 promoter.

Genomic footprinting on the Drosophila hsp26 promoter in isolated nuclei has shown that a TATA box binding factor is present before and after induction by heat shock, while three of the seven heat shock consensus sequences 5' of the gene are occupied (presumably by heat shock factor, HSF) specifically on heat shock. The sites of HSF interaction are separated by greater than 200 bp of which approximately 150 bp are bound to the surface of a nucleosome. The juxtaposition of these various macromolecules on the DNA suggests a basis for the major DNase I hypersensitive site 5' of hsp26 and a novel tertiary structure for the promoter complex.     

Naturally occurring transposable elements disrupt hsp70 promoter function in Drosophila melanogaster

Naturally occurring transposable element (TE) insertions that disrupt Drosophila promoters are correlated with modified promoter function and are posited to play a significant role in regulatory evolution, but their phenotypes have not been established directly. To establish the functional consequences of these TE insertions, we created constructs with either TE-bearing or TE-lacking hsp70 promoters fused to a luciferase reporter gene and assayed luciferase luminescence in transiently transfected Drosophila cells. Each of the four TEs reduces luciferase signal after heat shock and heat inducibility of the hsp70 promoter. To test if the differences in hsp70 promoter activity are TE-sequence dependent, we replaced each of the TEs with multiple intergenic sequences of equal length. These replacement insertions similarly reduced luciferase signal, suggesting that the TEs affect hsp70 promoter function by altering promoter architecture. These results are consistent with differences in Hsp70 expression levels, inducible thermotolerance, and fecundity previously associated with the TEs. That two different varieties of TEs in two different hsp70 genes have common effects suggests that TE insertion represents a general mechanism through which selection manipulates hsp70 gene expression.