We undertook a site-specific mutagenesis study to compare the role of individual elements of the ARID in the determination of sequence specificity. The structures of the Dri and p270 ARIDs are the best characterized among their respective types in regard to DNA interactions, so these domains were chosen for comparison. To test whether the presence of the threonine and phenylalanine residues in Helix 5 is sufficient to confer sequence specificity, we generated a mutant variant in which threonines and a phenylalanine were introduced into the appropriate positions in p270. The sequence of the resultant mutant, designated p270.TFT, is shown in Figure 5.
