Fig. 8. 5' Abd-B regulatory region, 5' iab-8 domain and models of regulation in the Abd-B^lac1 mutation. (A) The Abd-B m transcription unit (white boxes; HB, Homeobox), the upstream and downstream regulatory regions and the breakpoints of some Abd-B mutations are shown. Different DNA regions are marked as in Fig. 1. The iab-7 regulatory region is marked in red and the Fab-7 boundary as a light blue oval. The region in pink indicates the fragment that drives expression in PS13, and the region in green the possible location of the 5' iab-8 region. (B) Model 1. Scheme of the pairing between the exogenous and endogenous Fab-8/PRE/iab-8 elements in the Abd-B^lac1 mutation. This pairing may facilitate the interaction between iab-7 sequences and the lacZ gene and hinder the interaction of the 3' endogenous iab-8 sequences and the Abd-B endogenous promoter. (C) Model 2. The Fab-7 boundary pairs with the exogenous Fab-8 boundary. To simplify the figure, the possible pairing of PRE sequences has not been indicated (there is a PRE adjoining the Fab-7 boundary) (Mihaly et al., 1997). The iab-7 and endogenous 3' iab-8 sequences are now in the same domain, and active in PS12.