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Figure 4


Fig. 4. Anti-insulator activity in the Abd-B promoter. On the 2-B-Fab-8-A-5 construct (top diagram), the Fab-8 insulator was inserted between the two homeotic promoters. In this configuration both the IAB2 and IAB5 enhancers activate the Abd-B promoter, as CAT is expressed in the broad stripes, extending from parasegment 7 (black arrowhead) towards the posterior of the embryo (A), whereas no lacZ expression can be detected (B). To verify that IAB5 is activating expression from the Abd-B promoter, the IAB2 enhancer was removed to generate the B-Fab-8-A-5 construct (middle diagram). Transgenic embryos confirmed that IAB5 is indeed recruited the Abd-B promoter as CAT expression can be seen in a distinctive IAB5 pattern (C), whereas lacZ is not activated (D). To examine whether spacing had an effect on these interactions, a 1.6 kb {lambda}-spacer DNA was placed between the two homeotic promoters on the 2-B-1.6{lambda}-A-5 construct (bottom diagram). The addition of this {lambda}-spacer did not modulate the activation of expression from the Abd-B promoter by the IAB2 and IAB5 enhancers (E) and no lacZ expression is detected (F).