Three classes of C2H2 zinc finger proteins.

C2H2 zinc finger proteins probably comprise the largest family of regulatory proteins in mammals. Most zinc fingers bind to a cognate DNA. In addition to DNA, many of the proteins also bind to RNA or protein, and some bind to RNA only. The binding properties depend on the amino acid sequence of the finger domains and of the linker between fingers, as well as on the higher-order structures and the number of fingers. C2H2 zinc finger proteins contain from 1 to more than 30 figures. Based on the number and the pattern of the fingers, most of the proteins can be classified into one of three groups: triple-C2H2, multiple-adjacent-C2H2, and separated-paired-C2H2 finger proteins. In contrast to proteins with triple-C2H2 fingers, proteins with multiple-adjacent-C2H2 fingers can bind multiple, different ligands. Proteins with a number of separated-paired fingers bind to the target by means of only a single pair.