Figure 1.

Primary structures of typical KRAB-containing zinc-finger proteins, illustrating the range of domains they contain. Note that the number of zinc fingers among proteins in the family is very variable, ranging from 4 to over 34; only 8 are shown in each structure here, for simplicity. The KRAB domain consists of the A and B boxes; some proteins contain a variant called the b box. Some members of the family have a leucine-rich SCAN domain that allows homo- and hetero-dimerization with other SCAN-containing zinc-finger proteins. Several proteins have been found corresponding to each of the structures shown; they therefore probably represent distinct structural and functional subfamilies. N, amino terminus; C, carboxyl terminus.