The specificity residues of the ankyrin repeat family. The specificity residues (red) of p19-INK4D (CDN2D) are concentrated on one molecular face in the three-dimensional structure (Protein Data Bank: 1blx; complex with cyclin-dependent kinase [CDK6]). As predicted, many of these residues are in the binding site. Colors as in Figure 4. The specificity residues for p19 were calculated from the PFAM alignment of ankyrin repeats and then mapped onto each of the three ankyrin repeats (residues 41 to 72, 73 to 105, and 106 to 137) of P19; the cyan structure contains all three repeats.