Fig. 5. PSE1 and PSE2 can act as positive regulatory elements. Left column shows immunoperoxidase staining to detect β-gal protein in line P[en3]-tou and its derivatives and from P[en3]-enboth (embryos 10 hours AEL; anterior is leftwards, dorsal is upwards). Right column indicates wing discs stained for β-gal activity. Two things happen in embryos when the PSEs are removed from P[en3]-tou: (1) the intensity of the stripes decreases and (2) the β-gal background levels increase. In wing discs, removal of PSE2 causes some misexpression of β-gal in the anterior compartment in the wing pouch in P[en3]-touPSE2 wing discs. Similar results were seen in other discs. Deletion of PSE1 from P[en3] caused most of the β-gal activity in wing discs to be lost. Similar results were seen in other discs (data not shown). Deletion of PSE1 and PSE2 from P[en3]-en had no effect on the expression of β-gal at any stage examined.