Fig. 1. The HOMRE does not activate transcription in the same domain as the entire lab550 enhancer. The sequence of the lab550 enhancer is shown in A. The HTH-, LAB- and EXD-binding sites are shown in green, red and blue boxes, respectively (Grieder et al., 1997; Ryoo et al., 1999). The extent of the 48/95 HOMRE is indicated by the red arrows and the extent of the 50 bp element (see text) by the green arrows. Four MAD/MEDEA-binding sites are underlined and four CREs are boxed in blue. The repressor element shaded in orange. A GATA site is boxed in red and a HMG-binding site in green. Nucleotides conserved between the D. melanogaster lab550 enhancer and the corresponding element from D. hydei are printed in bold; non-conserved residues are not bold. The sequence stretch from 185 to 215 is not conserved between the two species. (B-D) The expression of endogenous lab (brown, B) is compared with the expression driven by lab550 (C; lab in blue, lab550 driven ß-GAL expression in brown) and the expression driven by the HOMRE 48/95 (D; lab in blue, HOMRE in brown) in stage 13 embryos. Clearly, lab550 mimics the expression of lab, whereas HOMRE-driven expression is mostly posterior to lab. (E-J) Using confocal microscopy, the expression of lab550 (green; E,G) and the HOMRE (green; H,J) is compared with endogenous lab (red; F,G,I,J) in stage 14 embryos. Expression levels were higher in later stages and it was not possible to use confocal microscopy in stage 13 embryos.