Proposed structure for the DNA-binding domain of the Myb oncoprotein based on model building and mutational analysis

Abstract

Myb-related proteins from plants to humans are characterized by a DNA-binding domain which contains two to three imperfect repeats of ˜50 amino acids each. Based on the evolutionary conservation of specific residues, secondary structural predictions suggest an arrangement of a helices homologous to that seen in the homeodomains, members of the helix-turn-helix family of DNA-binding proteins. We have used molecular modelling in conjunction with site-directed mutagenesis to test the feasibility of this structure. We propose that each Myb repeat consists of three a helices packed over a hydrophobic core which is built around the three highly conserved tryptophan residues. The C-terminal helix forms part of the helix-turn-helix motif and can be positioned into the major groove of B-form DNA, allowing prediction of residues critical for specificity of interaction. Modelling also allowed positioning of adjacent repeats around the major groove over an 8 bp binding site.