Structure and evolution of a pair-rule interaction element: runt regulatory sequences in D-melanogaster and D-virilis

Pair-rule genes serve two important functions during Drosophila development : they first initiate periodic patterns, and subsequently interact with eac h other to refine these patterns to the precision required for definition o f segmental compartments. Previously, we described a pair-rule input region of the runt gene. Here we further characterize this region through the use of reporter gene constructs and by comparison with corresponding sequences from Drosophila virilis. We find that many but not all regulatory properti es of this '7-stripe region' are functionally conserved. Moreover, the simi larity between these homologous sequences is surprisingly low. When compare d to similar data for gap gene input elements, our data suggest that pair-r ule target sequences are less constrained during evolution, and that functi onal elements mediating pair-rule interactions can be dispersed over many k ilobases. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.