The noncanonical Met residue is essential for binding to DNA. Various mutations in an ATHB33-GAL4AD fusion protein were assayed for their ability to bind to target DNA sequences using yeast one-hybrid assays; left section, binding to 2XPEE target sequences (−285 to −83) in sense orientation; right panel, binding to 2XPEE target sequences in antisense orientation. No AD, No AD included in construct; no HD, deleted for the HD; M to A, Met 49 to Ala substitution in the HD; M to F, Met 49 to Phe substitution in the HD; Full length, complete coding sequence of ATHB33 fused to GAL4AD; AD only, construct contained only the GAL4AD.