Repression of hsp70 heat shock gene transcription by the suppressor of hairy-wing protein of Drosophila melanogaster

The suppressor of hairy-wing [su(Hw)] locus of Drosophila melanogaster encodes a zinc finger protein that binds a repeated motif in the gypsy retroposon. Mutations of su(Hw) suppress the phenotypes associated with mutations caused by gypsy insertions. To examine the mechanisms by which su(Hw) alters gene expression, a fragment of gypsy containing multiple su(Hw) protein-binding sites was inserted into various locations in the well-characterized Drosophila hsp70 heat shock gene promoter. We found no evidence for activation of basal hsp70 transcription by su(Hw) protein in cultured Drosophila cells but observed that it can repress heat shock-induced transcription. Repression occurred only when su(Hw) protein-binding sites were positioned between binding sites for proteins required for heat shock transcription. We propose that su(Hw) protein interferes nonspecifically with protein-protein interactions required for heat shock transcription, perhaps sterically, or by altering the ability of DNA to bend or twist.