Amino acid alignments of Myb-related repeats display high conservation of structural residues and an acidic patch in the first helix. A. We created a multiple sequence alignment of Myb repeats using ClustalW and color coded the alignments based on conservation using the BioEdit program. Labeling of Myb-repeats indicates genus and species with the first two letters, followed by the protein name. For proteins containing multiple Myb-motifs, repeats are numbered starting from the N-terminus and identified after an underscore. Residues known to bind DNA of c-Myb (c-Myb DNAB) second repeat (R2) and third repeat (R3) are depicted in bold on the first two lines, those interacting with DNA bases are in black and those associating with the phosphate backbone are in grey. Note the high conservation of acidic residues in the first helix compared to c-Myb DNA-binding residues. Species and genus abbreviations: Hs = Homo sapiens, Dm = Drosophila melanogaster, Ce = Caenorhabditis elegans, Sc = Saccharomyces cerevisiae. B. The crystal structure of the c-Myb DNA-binding domain bound to DNA is shown . The first repeat (R1) is depicted in yellow, the second repeat (R2) in purple, and the third repeat (R3) in pink. The conserved acidic patch in the first helix of each repeat is highlighted in red, revealing a location on the solution side of the protein consistent with a protein-protein interaction motif. C. Myb-repeats from the solved c-Myb third repeat (c-Myb_R3) , yeast Rap1 first repeat (Rap1_R1) , and human Trf2 . For each repeat, one is looking down the barrel of the first helix (bottom) with the second helix on the left and the third helix on the right. The conserved acidic residues are depicted in red. Conserved salt bridges are shown between the acidic residue in the first helix (red) and a basic residue in the third helix (green).