Figure 1.

Paused/stalled Hox gene promoters display insulator activity. The Hox gene promoters were tested for their ability to block enhancer promoter interactions in transgenic assays. The Hox/lacZ fusions were cloned between IAB5 enhancer and white reporter gene. The IAB5-lacZ interaction was seen for all of the transgenic lines for Abd-B/lacZ (A), Ubx/lacZ (C), abd-A/lacZ (E), Antp/lacZ (G), lab/lacZ (I), and Scr/lacZ (K) as the classical PS10-14 staining was observed during lacZ probe in situ. The IAB5–white interaction was blocked in all stalled promoter-lacZ fusions like Abd-B/lacZ (B), Ubx/lacZ (D), Antp/lacZ (H), and lab/lacZ (J) lines as no white in situ signal was observed in the IAB5 pattern. The nonstalled promoter-lacZ fusions like abd-A/lacZ (F) and Scr/lacZ (L), however, did show the IAB5 pattern when stained for white probe, as they did not show any insulator activity. The weak staining in the head regions is due to the P-transformation vector used in these experiments (Small et al. 1992). The embryos are aligned anterior to the left and posterior to the right.