The E boxes (E1, E2, E3) in the minimal promoter region, pZJ23 [−385 to −1] (line 1), were examined using site-directed mutagenesis. GFP reporters containing the mutated sites revealed tissue-specific requirements for each E box (lines 2,4,5). A GFP reporter made with a mutated GT box, which has the same base composition as an E box, leads to a decrease in expression in vulval muscles (line3). The mutated sequence in each construct is underlined and the specific mutated nucleotides are in lower case. Black bars indicate the sequences that are not changed in the mutagenesis. Refer to Fig. 3 for details on examining the GFP expression pattern.