Basal level transcription of the human hsp86 gene is directed by intron-based elements

The heat shock response includes the syntheses of three major size-classes of heat shock proteins (hsps) designated as class 20, 70 and 90 hsps, respectively. In contrast to the class 20 and 70 hsp genes, those coding for the class 90 hsps are already actively transcribed in the non-induced state.

We have shown that the increased basal level transcription of the human hsp86 gene depends on the presence of the first intron. Furthermore, intron 1 of the hsp86 gene was also capable of conferring increased basal level transcription on the human hsp70 promoter. Finally, the intron I-based sequence elements of the hsp86 gene mediated an effective rescue of 5'-truncated hsp70 and hsp86 promoters. In contrast, such a rescue of inactivated promoters was not obtained with the viral SV40 gene enhancer which is often also capable of stimulating basal level expression.

Element(s) which direct the basal transcription of the human hsp86 gene at normal physiological temperatures are located within the first intron of the gene. It is conceivable that this intron-dependent activation of basal hsp86 transcription reflects a fundamental requirement for this protein in the context of cellular growth and metabolism under non-stress conditions.