Hsp70 promoter fragment and an AUG initiator codon drive expression of a 2.3 kb Sh fragment containing the last 40bp of exon 15 (including the 5' donor site), all of intron 15/16 (2.2kb) and the first 40bp of exon 16 (including the 3' acceptor site) fused to the lacZ coding region. A 740bp Sh fragment containing the 700bp of intron 18/19 immediately 5' to the exon 19 3' acceptor site and the first 40bp of exon 19 (including the 3' splice site) is fused downstream of the lacZ gene.