Previous studies on the regulation of the segmentation gene even-skipped (eve) have centered on the transcription of stripe 2. Here, we characterize another enhancer module contained within the complex eve promoter that directs expression of stripes 3 and 7. This enhancer is ~ 500 bp in length and maps ~ 3.3 kb upstream of the transcription start site. The stripe 3 + 7 enhancer appears to be regulated by one or more ubiquitously distributed activators, including components of a TAK-Stat pathway. The two-stripe pattern results via multiple tiers of repressors which delimit this ubiquitous activation. The zinc finger repressor hunchback appears to be responsible for establishing the anterior border of stripe 3 and the posterior border of stripe 7. knirps, a member of the nuclear receptor family of transcription factors, appears to establish the posterior border of stripe 3 and the anterior border of stripe 7. Activator and repressor proteins bind in vitro to several sites within the enhancer. These findings suggest a general model for the regulation of segmentation stripes, whereby enhancers integrate positional information provided by broadly distributed activators and spatially restricted repressors.
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