Saturation mutagenesis of AP-1 dependent elements. (A,B) Results from saturation mutagenesis of an AP-1-dependent sequence: (x-axis) nucleotide position in the element; (vertical gray box) position of the AP-1 core motif; (y-axis) expression of point mutants relative to the parental sequence. Point mutations were created in the context of either the wild-type AP-1 site parent (blue) or the AP-1mut site parent (red). Substitutions that were not significantly different from wild-type are faded. The dashed box in A shows a cluster of mutants that affect expression only when the wild-type AP-1 binding site is present, and are thus designated as “interacting” substitutions. The dashed box in B shows a cluster of mutants in the first 10 bp that reduce expression in both the WT and AP-1mut background; thus they contribute to the activity of the sequence “independent” of AP-1. (C) The spatial distributions of independent (gray) and interacting (tan) features in the 20 sequences subjected to saturation mutagenesis. Interacting features tend to occur closer to the AP-1 core motif.
