Efficient transcription of a Caenorhabditis elegans heat shock gene pair in mouse fibroblasts is dependent on multiple promoter elements which can function bidirectionally.

A divergently transcribed pair of Caenorhabditis elegans hsp16 genes was introduced into mouse fibroblasts by stable transfection with vectors containing bovine papillomavirus plasmid maintenance sequences and a selectable gene. The hsp16 genes were transcriptionally inactive in the mouse cells under normal growth conditions and were strongly induced by heat shock or arsenite. In a cell line with 12 copies of the gene pair, there were estimated to be more than 10,000 hsp16 transcripts in each cell after 2 h of heat shock treatment. The hsp16 transcript levels were more than 100 times higher than those of a gene with a herpes simplex virus thymidine kinase gene promoter carried on the same vector. A single heat shock promoter element (HSE) could activate bidirectional transcription of the two hsp16 genes when placed between the two TATA elements, but the transcriptional efficiency was reduced 10-fold relative to that of the wild-type gene pair. Four overlapping HSEs positioned between the two TATA elements resulted in inducible bidirectional transcription at greater than wild-type levels. The number of HSEs can therefore be a major determinant of the promoter strength of heat-inducible genes in mammalian cells. Partial disruption of an alternating purine-pyrimidine sequence between the two hsp16 genes had no significant effect on their transcriptional activity.