Combinations of maternal-effect and gap proteins control individual pair-rule stripe formation

Regulation of a pair-rule stripe: combinatorial control of an independent cis-acting regulatory element. (a) The regulation of the eve stripe 2 cis-acting regulatory element controls the formation of the second stripe of eve expression in the early embryo, just one of seven stripes of eve expression. (b) The stripe forms within the domains of the Bicoid and Hunchback proteins and at the edge of the Giant and Krüppel gap proteins. Bcd and Hb are activators, Gt and Kr are repressors of the stripe. (c) The eve stripe 2 element is just one of several cis-acting regulatory elements of the eve gene, each of which controls different parts of eve expression. The eve stripe 2 element spans from about 1 to 1.7 kb upstream of the eve transcription unit. (d) Within the eve stripe 2 element, several binding sites exist for each transcription factor (repressors are shown above the element, activators below). The net output of this combination of activators and repressors is expression of the narrow eve stripe.