Figure 5

Relative entropy analysis of canonical positions in 28,442 C₂H₂ zinc fingers. (a) Positions in the graph are shown in the order found in Pfam and numbered by convention (where -1 is the residue N-terminal to the α-helix). Note that the y-axis scale is different from Figs. 1 and 2 due to the almost invariant zinc(II)-binding residues (-10, -7, +7 and +11). Blue and green arrows indicate the seven predicted specificity-determining positions. (b) The middle zinc finger of Zif268 bound to DNA (purple) is shown, with the Zn(II) atom as a pink sphere [43]. (c) The residues in contact with the DNA from all three zinc fingers of Zif268 are rendered in spheres. The DNA-binding positions group into variable, specificity-determining positions (blue and green spheres) projecting into the major groove of the DNA, and conserved positions that enhance affinity to DNA but do not affect specificity (orange and red spheres). Rendered with PyMOL from PDB entry 1A1I.