Figure 3.
Effect of BoxG18A mutation on NagC binding sequence. The consensus sequence, including alternative bases at some sites, for a 23-bp NagC-binding Box element is shown at the top [31]. The four underlined bases are the only ones that are invariant across all such elements [31], and mutagenesis has shown that these four are also the most important for binding NagC [38]. The next row shows the ancestral BoxG1 sequence. The bottom two rows show the effect of inserting an extra adenine, as in the evolved BoxG18A allele, when viewed as shifting the sequence either to the left or to the right. The former eliminates the invariant T at position -5. The latter removes agreement with the consensus at position +11.