Characterized binding sites evolve more slowly than the promoters in which they are found. A. Histogram of the rate of evolution (estimated by maximum parsimony) in characterized Gal4p binding sites and randomly chosen sequences of the same length (17 basepairs) from the same promoters. B. Differences in the mean rate of evolution in motifs and the mean rate in the promoters in which they are found. Grey boxes represent the average in binding sites; unfilled boxes represent the average over the promoters in which the motifs are found (see methods). Error bars represent exact 95 % confidence intervals for a Poisson distribution.