DNA-binding properties of HAT3.1, a PHD-finger homeodomain protein of Arabidopsis.

IVANA L. VIOLA; DANIEL H. GONZALEZ

Rosario. Santa Fe, Argentina.

Congreso; XLII Reunión Anual de la Sociedad Argentina de Investigación en Bioquímica y Biología Molecular,; 2006

SAIB

HAT3.1 is a member of the PHD-finger homeodomain protein family found only in plants. In this study, hydroxyl radical footprinting experiments and yeast one-hybrid assays indicated that HAT3.1 shows a preference for the sequence T(A/G)(A/C)ACCA, different from those bound by other homeodomains. Binding was dependent on homeodomain residues located at positions 50, 51 and 54, that is the same positions that usually participate in DNA binding in most homeodomains. The study of the interaction of mutants at these positions with DNA with nucleotide changes at specific sites suggested that His51 and Lys50 most likely interact with nucleotides 2 to 4 and 5 to 6, respectively, while Trp54 would establish contacts with position 4. In addition the DNA binding activity is increased at low pH. Since replacement of His51 with Asn produced a protein non-responsive to pH changes, it can be speculated that the protonation state of His51 modulates the DNA binding efficiency of HAT3.1. Finally, a model in which the sequence T(A/G)(A/C)ACC can be assimilated to TAATCC bound by other homeodomains is postulated. The presence of His51 and Trp54 represents an innovation among homeodomain structures. The fact that the HAT3.1 homeodomain is able to interact with specific DNA sequences is an evidence of the inherent plasticity of the homeodomain as a DNA binding unit.