To test the contribution of the invariant residues in the ARID structure, specific invariant residues were changed to the small neutral residue alanine in the ARIDs of both Dri and p270. The resultant wild-type and mutant peptides were translated in vitro, and their DNA-binding affinity was assessed using a sensitive and quantitative DNA affinity column chromatography assay described previously (9,11). Because the DNA is in large excess, the assay is unbiased with respect to sequence specificity. The results are shown in Figure 10.
