FIGURE 6.

The 23-bp element is sufficient for heme response. A, schematic diagram of a concatamer of six direct repeats of the 23-bp element fused to the egl-18 basal promoter. This chimeric promoter was placed upstream of gfp and the unc-54 3′ UTR. B, transgenic C. elegans strains expressing either egl-18::gfp or egl-18(+23)::gfp were placed in medium supplemented with either 4 or 100 μm heme for 120 h, and GFP expression in the worms was analyzed by microscopy. Scale bars = 100 μm. C, GFP was quantified in C. elegans transformed with egl-18::gfp or egl-18(+23)::gfp and supplemented with 2 or 40 μm heme. The y axis is the GFP level in arbitrary units. ***, p < 0.001.