Separate regulatory elements for the heat-inducible and ovarian expression of the Drosophila hsp26 gene.

We have constructed and transformed into the D. melanogaster germ line a series of hsp26 deletion variants. We show that the region -728 to +14 contains all of the cis-acting sequences necessary for the developmental and heat-inducible transcription of hsp26. Sequences upstream of -341 are not required for heat-inducible expression but are required for ovarian expression. Conversely, sequences between -351 and -53 are unnecessary for ovarian expression but are needed for maximal heat-inducible expression. We conclude that most, or all, of the cis-acting regulatory sequences required for hsp26 gene expression during oogenesis are physically separable from those required for heat-inducible expression. These results suggest that different trans-acting factors bind at different regulatory sites in the 5'-flanking region of the gene, thus activating its transcription.