P{A92} in inserted into the first intron of Ubx, at coordinate -34kb of FBrf0040194. The Ecol\lacZ gene is transcribed in the opposite orientation to Ubx. Transcriptional analysis indicates that the Ubx transcripts initiate but do not continue to their proper 3' end.
Δ2-3-induced mobilization of the P{A92} insert causes reversions as well as generating different bithorax/postbithorax phenotypes from the original Ubxlac1 insertion.