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This paper describes the detailed three-dimensional structures of two
zinc-finger domains from the yeast transcription factor SWI5, calculated using
the results of the n.m.r. experiments described in the accompanying paper. The
structure of finger 2 is essentially similar to those previously obtained by
others for isolated, synthetic single zinc-finger domains in solution, and for
the three zinc-finger peptide Zif268 in its crystalline complex with DNA. The
N-terminal half of the sequence forms a two-stranded, irregular beta-sheet
containing both of the metal-binding cysteine residues, while the remainder of
the structure forms a helix. Approximately the first half of this helix is
alpha-helical, whereas the C-terminal portion, including the two metal-binding
histidine residues, is 3(10) helical. Four invariant hydrophobic residues form a
core to the structure. In contrast to all previously described structures of
zinc-finger domains, finger 1 has an additional strand in the beta-sheet, formed
by residues N-terminal to the formal start of the finger motif. This additional
strand plays a role in stabilising the folded form of finger 1, since a
two-finger peptide lacking the N-terminal residues showed folded structure in
finger 2 but not in finger 1.
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