2.5kb fragment containing an Hsp70 promoter, ATG and 940bp coding sequence are fused in frame to a fragment of the P-element (nucleotides 1944 to 2183) which includes the third intron, followed by lacZ reporter sequence and an SV40 polyadenylation site. The intron sequence must be spliced out in order for functional lacZ protein to be produced; no β-galactosidase activity was observed in either the soma or germline.