An Hsp70 promoter drives expression of a ribozyme that is designed to cleave prd mRNA at a CUU site between nucleotides +304 and +305, downstream of the initiator ATG and 27 nucleotides upstream of the 5' intron/exon border. The ribozyme consists of a 24 base hammerhead catalytic centre flanked by 8-11 bases complementary to the prd mRNA target region.
Heat induced expression at an early stage of development (about 2.5 hours) generated a pair-rule phenotype in about 15% of embryos and a mild prd-like phenotype in 25% of embryos. Heat induced expression after 4-5 hours of development (the time of prd expression in the head segments) causes grossly abnormal larval head structures. Ventral organ and maxillary chemosensory organs are missing and the dorsal cirri row is reduced.