Structural and Thermodynamic Characterization of the DNA Binding Properties of a Triple Alanine Mutant of MATα2 (original) (raw)

homeodomain bound to DNA, the a1/␣2 heterodimer bound to DNA, and the ␣2/MCM1 heterotetramer bound to DNA [9-11]. The DNA binding domain of ␣2 adopts a typical homeodomain fold [11][12][13], with a compact three-helix globular domain that contacts major groove bases and the DNA backbone, mainly through the third helix, and an extended N-terminal arm that inserts into School of Medicine 725 North Wolfe Street the DNA minor groove. The contacts between ␣2 and DNA are nearly identical in all three crystal structures. The ␣2 protein contacts four base pairs in the DNA major groove using three side chains in helix 3: Ser50, Asn51, Department of Biochemistry Rutgers University and Arg54 ). Ser50 forms two watermediated hydrogen bonds with A4 and T5, Arg54 con-Piscataway, New Jersey 08854 tacts G6 with two direct hydrogen bonds, and Asn51 forms bidentate hydrogen bonds with A38. Asn51, which is an invariant homeodomain residue, forms identical Summary contacts in other homeodomain-DNA structures [11][12][13]. Additional side chains in helix 3 of ␣2 make DNA Triply mutated MAT␣2 protein, ␣2-3A, in which all phosphate backbone contacts, which help to position three major groove-contacting residues are mutated the recognition helix of ␣2 in the DNA major groove. In to alanine, is defective in binding DNA alone or in com-

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