Fig. 3. PTS facilitates and restricts enhancer activity to a single promoter. Constructs W32 and W81 were tested. The former contains an FRT flanked PTS and Fab-8, and the IAB8 enhancer, where as the latter contains FRT flanked PTS and suHw, plus a 1.0 kb IAB5 enhancer. Large orange arrowheads indicate FRT sites. (A,B) A representative line exhibiting a selective IAB8-w interaction is shown. (C,D) The same strain after removal of the Fab-8 insulator and the PTS by Flp-mediated recombination (Golic and Lindquist, 1989). There is a severe reduction of IAB8-w interaction with the accompanying activation of lacZ. (E,F) Most transgenic strains carrying the W81 display an IAB5-lacZ interaction as shown here. (G,H) The same strain after Flp-FRT analysis. Note the reduction of IAB5-lacZ interaction and the concomitant appearance of IAB5-w interaction.