Upstream elements necessary for optimal function of the hsp 70 promoter in transformed flies.

Deletion mutants of the Drosophila hsp 70 promoter region have been fused to a truncated Drosophila Adh gene lacking its own promoter. These fusion genes were introduced into the Drosophila genome using the P-element transformation system. S1 mapping of fusion transcripts in transformed flies shows that their expression is completely dependent on the function of the hsp 70 promoter, and that 97 bp of hsp 70 5'-flanking DNA is sufficient to induce transcription upon heat shock to a level similar to that of the wild-type hsp 70 gene. By contrast, a deletion containing 68 bp of 5'-flanking DNA is only inducible to a low level even though this deletion retains the consensus sequence, which is sufficient for induction and maximal expression of this gene in COS cells and Xenopus oocytes. A sequence centered at -125 with the potential for forming an S1 nuclease-sensitive structure does not affect inducibility or efficiency of expression.