Zinc finger motif

A single protein (one polypeptide chain) binds DNA through several consecutive zinc finger motifs.

This is a fragment (amino acid residues 1 to 101) of the TFIIIA transcription factor, from the frog Xenopus laevis, bound to 15 bp of the 5S RNA gene.


How many zinc finger motifs are shown?

The structure common with other proteins, and hence called the motif, consists in this case of a peptide segment in alpha helix and two in antiparallel beta sheet, in which there are 4 amino acids (2 Cys and 2 His) whose sidechains coordinate the Zn2+ ion; this kind of zinc finger is so called C2H2.    The atoms coordinating Zn (N in His and S in Cys) are highlighted.

Again, several consecutive C2H2 zinc finger motifs in the same polypeptide chain.

From the same protein, TFIIIA.


How many zinc finger motifs are shown?
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Another kind of zinc finger motif.

Human oestrogen receptor, bound to DNA.

In this case, the protein has a single zinc finger but forms a dimer when bound to DNA.

In addition, the motif has a different structure: two Zn2+ ions, each one coordinated by a helix and a loop, through the sidechains of 4 cysteines for each Zn ion.
This kind of motif is called a C4 zinc finger.