FIG. 3.
CtBP repression is dependent on the presence of adjacent activators. (A) Expression pattern of the CtdU(−55) reporter containing two Twist and two Dorsal binding sites immediately 5′ of the UAS sites situated at −55 bp. (B) Gal4-CtBPL effectively represses transcription from the CtdU(−55) reporter, creating an unstained central gap (bracket). (C) Gal4-CtBPL does not repress transcription of the CRTU(−55) transgene in embryos at stages 6 and later in development. In the embryo shown (stage 8), staining posterior to the bracket is similar to that within the central domain, where Gal4-CtBP is expressed. (D) In embryos of similar age containing a reporter with proximal Twist and Dorsal sites in addition to the distal activator sites [CRTtdU(−55)], Gal4-CtBPL strongly represses Twist and Dorsal activities (bracket), leaving residual expression in the central region of the embryo, similar to that shown in panel C.