PROTEIN MOTIFS .5. ZINC FINGERS

The term zinc finger was first used to describe a 30-residue, repeated sequence motif found in an unusually abundant Xenopus transcription factor, It was proposed that each motif is folded around a central zinc ion to form an independent minidomain and that adjacent zinc fingers are combined as modules to make up a DNA-binding domain with the modules ''gripping'' the DNA (hence the term finger), We now know that these proposals were correct and that these DNA-binding motifs are found in many eukaryotic DNA-binding proteins. More recently, crystal structures of three different complexes between zinc finger domains and their target DNA binding sites have revealed a remarkably simple mode of interaction with DNA. The simplicity of the zinc finger structure, and of its interaction with DNA, is a very striking feature of this protein domain, After the discovery of the zinc finger motif, patterns of potential zinc ligands have been found in several other proteins, some of which also bind to DNA. Structural studies of these domains have revealed how zinc can stabilize quite diverse protein architectures, In total, 10 such small zinc-binding domains have been studied structurally. These form a diverse collection, but each in turn has been termed a zinc finger motif-although clearly what they have in common is only their zinc-binding property, which stabilizes an apparently autonomously folded unit.