Zinc fingers

Within the past year, the first three-dimensional structures of zinc-finger domains have become available. Using two-dimensional NMR methods, the solution conformations have been determined for three classes of zinc-finger peptides: the single-finger domains of the yeast transcriptional activators ADR1 and SWI5 and of the Xenopus protein Xfin, which are all homologous with the prototypal fingers of the transcription factor TFIIIA (CC/HH zinc fingers); the metal-binding site of a retroviral protein derived from the gag gene (CC/HC zinc finger); and the DNA-binding domain of the glucocorticoid receptor, a member of the superfamily of steroid/thyroid hormone receptors (two CC/CC zinc fingers). Whereas the TFIIIA and retroviral zinc fingers are independent protein domains, the DNA-binding site of the steroid-hormone receptors forms a single folded structure which exhibits strong interactions between the two fingers. The peptide conformations of the various classes of zinc fingers are entirely different.