Fig. 1. Schematic representation of the SpEndo16 promoter. (A) Relative position of 56 binding sites within the 2.2 kb region that has been shown to drive SpEndo16 expression (Yuh et al., 1994). Twelve unique factors (brown ovals) each interact with only one binding site, six `common factors' (colored rectangles) interact with a few identical (or nearly identical) binding sites, and the structural protein GCF1 (blue ovals) interacts with 23 sites in the SpEndo16 promoter. [Figure adapted from Yuh and Davidson (Yuh and Davidson, 1996)]. (B) Binding sites within the SpEndo16 promoter are clustered into six functionally distinct modules that serve to activate (+) or repress (-) transcription. (C) Logic circuit diagram showing interactions between binding sites within modules A and B of the SpEndo16 promoter based on transient expression assays [Figure adapted from Yuh et al. (Yuh et al., 2001a). Note that binding sites in modules A and B interact extensively.