Fig. 1. The brk regulatory region contains multiple elements that mediate activation. (A) The brk promoter with arrows indicating transcription start sites for brk and unc-119. Scale is in kb and EcoRI sites (R1) are marked. Filled fragments drive expression in wing discs and embryos after stage 11; open fragments are transcriptionally inactive at these stages. The B14 construct of Muller et al. (Muller et al., 2003) is in gray, with `r' signifying repressor elements and E the activator. (B-I) Reporter expression in wing discs oriented anterior upwards, ventral leftwards. (B) The brk^X47 enhancer trap reproduces wild-type brk pattern. (C,D) L1 and L2 are non-overlapping promoter fragments that direct patterns resembling endogenous brk. L1 drives low-level expression and the image was enhanced by increased exposure time. (E) L4 does not display detectable expression. (F) L5 is expressed strongly and excluded from only a narrow central domain. The central stripe of expression corresponds to the AP compartment boundary, where pMad levels are reduced (Tanimoto et al., 2000). (G,H) L6 and L7 also drive laterally restricted expression. L6 directs expression at lower levels than L7, and was enhanced by increasing exposure time. (I) Expression of L8 cannot be detected. (J-N) Reporter expression in late stage 12/13 embryos, oriented laterally. (J,K) Both L1 and L2 reporters mimic brk expression in ventral and lateral stripes in the ectoderm. (L) No embryonic expression is detected with L4. (M,N) L6 and L7 reporters can be detected in a brk-like pattern in the ectoderm and midgut.