The potential for differences in the overall structure of the p270 and Dri ARIDs was probed by introducing changes into the aromatic scaffold of the two domains. Within the core consensus sequence, there are five invariant amino acids that are almost identically spaced across each ARID. These are indicated by red text in Figure 1 and dots in Figure 4, and include a tryptophan (W) in Helix 4, a tyrosine (Y) in Helix 5 and a proline (P) in Loop 1. The presence of a series of invariant aromatic residues has been recognized as a structural scaffold in other helix–turn–helix motifs, including the DNA-binding motif in c-Myb and the homeodomain (35,36).
