A significant difference between the way the p270 and Dri ARIDs interact with DNA is that the p270 ARID has an additional large minor groove interaction site just upstream of Helix 0 (15). We considered the possibility that this region of 15 amino acids interacts strongly and non-specifically with DNA in a way that masks potential sequence-specificity in p270. We therefore deleted this segment in the p270.L2.TFT chimera to generate a new construct designated p270.ΔL2.TFT. The DNA-binding affinity of this fragment is reduced still further, confirming that the N-terminal region contributes significantly to DNA contact. However, the peptide still shows little or no selection for specific fragments (Figure 7). This argues against the possibility that sequence selectivity was transferred by the introduction of the Loop 2 and Helix 5 residues of Dri, but was masked by the unique N-terminal contact region of p270.
