Expression of Hr4 is driven by Hsp70 promoter sequences.
Most Hr4Hsp70.PK flies heat shocked in late L3 fail to initiate metamorphosis and die as L3.
Hr4Hsp70.PK partially rescues Hr41
Hr4Hsp70.PK rescues development of about 15% of Hr41 homozygotes through metamorphosis to the pharate adult stage.