Finger proteins and DNA-specific recognition: distinct patterns of conserved amino acids suggest different evolutionary modes.

Finger proteins, the first example of which was Xenopus TFIIIA, share Zn2+ finger-like folded domains capable of binding to nucleic acids. A large number of this type of protein have been characterised from diverse organisms, indicating a wide evolutionary spread of the DNA-binding fingers. At least two classes of finger proteins may be distinguished. Class I proteins contain variable numbers of the tandemly repeating TFIIIA-like finger motif, (Y/F-X-C-X2-4-C-X3-F-X5-L-X2-H-X3-H). Class II finger proteins display a single (C-X2-C-X13-C-X2-C) motif and a facultative second putative finger. The relation between the structure of finger proteins and their recognised DNA sequences is discussed.