Fig. 5. Gl regulates pros transcription. (A) Gl protein binds specifically to a sequence present in the mini-enhancer. (Left) The sequence is aligned with a characterized Gl-binding site in the Rh1 promoter. Conserved nucleotides are highlighted in red. A mutated version of the pros site is shown, with altered nucleotides in blue. (Right) A mobility-shift gel showing a complex that contains Gl protein and labeled Rh1 DNA. Each reaction also contained a 100x molar excess of an unlabelled competitor DNA, as indicated at the top, except for the leftmost lane, which did not contain any competitor. (B-B'') gl^60j mutant cells are marked with cytoplasmic GFP (green), whereas Gl⁺ cells are unmarked in a genetically mosaic larval eye disc. Nuclear Pros protein was visualized by antibody (purple). Gl⁺ cells that normally express Pros appear as non-ringed purple, whereas gl^60j cells that normally express Pros appear as white or purple, ringed in green. gl^60j cells that express undetectable or very low levels of Pros appear as hollow green rings or green rings with a weak white signal (see B''). (C-C'') A large clone of gl^60j mutant cells is marked by GFP (green) in the pupal eye. Cell morphology is visualized by the β-catenin protein Arm (purple). Arrowheads indicate the morphologies of wild-type cone cells. Arrows indicate gl^60j cone cells that exhibit altered sizes and morphologies. (D-D'') Transgenic mini-enhancer-lacZ reporter expression (green) in an eye disc counterstained for Pros protein (purple). The mini-enhancer has its Gl-binding site mutated, which induces very weak or no β-gal expression in Pros-positive cells.