sites (Figure S4A in Additional file 1). This global observation, however, does not rule out the possibility that a weaker match at some sites is specifically preserved to ensure dose-specific TF binding. This may be the case, for example, for Drosophila Bric-à-brac motifs, which exhibited no correlation between motif load and PWM score (Figure S4B in Additional file 1), consistent with the known dosage-dependent function of Bric-à-brac in embryo patterning [41].
