A consensus sequence polymer inhibits in vivo expression of heat shock genes.

Promoter function for hsp70 gene expression in Drosophila melanogaster was studied with an in vivo competition assay. A polymer of 40 tandem copies of the pair of regulatory elements of the hsp70 gene was constructed and cloned into a plasmid vector. Various marked genes were cotransfected with the polymer plasmid into Schneider line 2 cells, and their expression was determined by enzyme activity measurements. The polymer dramatically inhibited expression of cotransfected hsp70, hsp26, and hsp83 genes, but not cotransfected copia and histone genes. Our results indicate that in vivo, a trans-acting, positive regulatory factor, which can be titrated by heat shock consensus sequences, is required for activation of heat shock genes and is specific for these genes; the coordinate induction of different heat shock genes appears to be mediated by similar, but not identical, interactions of the trans-acting induction factor and the cis-acting heat shock consensus sequences; and the uninduced or basal level expression of the transfected hsp70 gene is also due to interaction of the consensus sequence with a positively acting factor.     

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.     

The heat shock consensus sequence is not sufficient for hsp70 gene expression in Drosophila melanogaster.

A hybrid gene in which the expression of an Escherichia coli beta-galactosidase gene was placed under the control of a Drosophila melanogaster 70,000-dalton heat shock protein (hsp70) gene promoter was constructed. Mutant derivatives of this hybrid gene which contained promoter sequences of different lengths were prepared, and their heat-induced expression was examined in D. melanogaster and COS-1 (African green monkey kidney) cells. Mutants with 5' nontranscribed sequences of at least 90 and up to 1,140 base pairs were expressed strongly in both cell types. Mutants with shorter 5' extensions (of at least 63 base pairs) were transcribed and translated efficiently in COS-1 but not at all in D. melanogaster cells. Thus, in contrast to the situation in COS-1 cells, the previously defined heat shock consensus sequence which is located between nucleotides 62 and 48 of the hsp70 gene 5' nontranscribed DNA segment is not sufficient for the expression of the D. melanogaster gene in homologous cells. A second consensus-like element 69 to 85 nucleotides upstream from the cap site is postulated to be also involved in the heat-induced expression of the hsp70 gene in D. melanogaster cells.     

Functional Analysis of Drosophila HSP70 Promoter with Different HSE Numbers in Human Cells

The activation of genetic constructs including the Drosophila hsp70 promoter with four and eight HSE sequences in the regulatory region has been described in human cells. The promoter was shown to be induced at lower temperatures compared to the human hsp70 promoter. The promoter activity increased after a 60-min heat shock already at 38°C in human cells. The promoter activation was observed 24 h after heat shock for the constructs with eight HSEs, while those with four HSEs required 48 h. After transplantation of in vitro heat-shocked transfected cells, the promoter activity could be maintained for 3 days with a gradual decline. The promoter activation was confirmed in vivo without preliminary heat shock in mouse ischemic brain foci. Controlled expression of the Gdnf gene under a Drosophila hsp70 promoter was demonstrated. This promoter with four and eight HSE sequences in the regulatory region can be proposed as a regulated promoter in genetic therapeutic systems.     

Positive and negative regulation of basal expression of a yeast HSP70 gene.

The SSA1 gene, one of the heat-inducible HSP70 genes in the yeast Saccharomyces cerevisiae, also displays a basal level of expression during logarithmic growth. Multiple sites related to the heat shock element (HSE) consensus sequence are present in the SSA1 promoter region (Slater and Craig, Mol. Cell. Biol. 7:1906-1916, 1987). One of the HSEs, HSE2, is important in the basal expression of SSA1 as well as in heat-inducible expression. A promoter containing a mutant HSE2 showed a fivefold-lower level of basal expression and altered kinetics of expression after heat shock. A series of deletion and point mutations led to identification of an upstream repression sequence (URS) which overlapped HSE2. A promoter containing a mutation in the URS showed an increased level of basal expression. A URS-binding activity was detected in yeast whole-cell extracts by a gel electrophoresis DNA-binding assay. The results reported in this paper indicate that basal expression of the SSA1 promoter is determined by both positive and negative elements and imply that the positively acting yeast heat shock factor HSF is responsible, at least in part, for the basal level of expression of SSA1.