The P{IT1} element contains a gene trap cassette that consists of a hh fragment (nucleotide position 11,206-11,353) containing a putative lariat signal, 3' splice acceptor site and the 5' end of exon 2, fused to the 5' end of the lacZ reporter coding sequence (lacking the initiation codon). An Hsp70 polyadenylation signal is fused downstream of the lacZ coding sequence.