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Zinc Fingers, Zinc Clusters, and Zinc Twists in DNA-Binding Protein Domains
Bert L. Vallee, Joseph E. Coleman and David S. Auld
Proceedings of the National Academy of Sciences of the United States of America
Vol. 88, No. 3 (Feb. 1, 1991), pp. 999-1003
Published by: National Academy of Sciences
Stable URL: http://www.jstor.org/stable/2356114
Page Count: 5
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We now recognize three distinct motifs of DNA-binding zinc proteins: (i) zinc fingers, (ii) zinc clusters, and (iii) zinc twists. Until very recently, x-ray crystallographic or NMR three-dimensional structure analyses of DNA-binding zinc proteins have not been available to serve as standards of reference for the zinc binding sites of these families of proteins. Those of the DNA-binding domains of the fungal transcription factor GAL4 and the rat glucocorticoid receptor are the first to have been determined. Both proteins contain two zinc binding sites, and in both, cysteine residues are the sole zinc ligands. In GAL4, two zinc atoms are bound to six cysteine residues which form a "zinc cluster" akin to that of metallothionein; the distance between the two zinc atoms of GAL4 is ≈3.5 Å. In the glucocorticoid receptor, each zinc atom is bound to four cysteine residues; the interatomic zinc-zinc distance is ≈13 Å, and in this instance, a "zinc twist" is represented by a helical DNA recognition site located between the two zinc atoms. Zinc clusters and zinc twists are here recognized as two distinctive motifs in DNA-binding proteins containing multiple zinc atoms. For native "zinc fingers," structural data do not exist as yet; consequently, the interatomic distances between zinc atoms are not known. As further structural data become available, the structural and functional significance of these different motifs in their binding to DNA and other proteins participating in the transmission of the genetic message will become apparent.
Proceedings of the National Academy of Sciences of the United States of America © 1991 National Academy of Sciences