 Heatmap of the tolerance to amino acid substitutions in WT transactivation domain sequences. The tolerance of a mutation is defined as the fraction of functional sequences over all the sequences when a specific substitution was performed. The columns (amino acid in a WT TAD that is substituted) are ordered according to decreasing tolerance (from left to right) and the rows (amino acid into which a residue in the WT TAD is substituted for) are ordered according to decreasing tolerance (from bottom to top). The cells are colored on a green to red gradient for high to low tolerance respectively. Empty tiles represent data points not present in the library 