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Title
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Structure of the B-Myb DNA-binding domain in solution and evidence for multiple conformations in the region of repeat-2 involved in DNA binding: implications for sequence-specific DNA binding by Myb proteins.
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Authors
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M.D.Carr,
U.Wollborn,
P.B.McIntosh,
T.A.Frenkiel,
J.E.McCormick,
C.J.Bauer,
K.H.Klempnauer,
J.Feeney.
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Ref.
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Eur J Biochem, 1996,
235,
721-735.
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PubMed id
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Abstract
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A range of double and triple resonance heteronuclear NMR has been used to obtain
nearly complete sequence-specific 15N, 13C and 1H resonance assignments for a
110-residue protein corresponding to the B-Myb DNA-binding domain (B-MybR2R3)
and to determine its secondary structure in solution. The protein was found to
contain two stable helices in repeat-2 (R2) and three in repeat-3 (R3),
involving residues K12-K24 (R2-1), W30-H36 (R2-2), E64-V76 (R3-1), W81-L87
(R3-2) and D93-K105 (R3-3). In addition, the chemical shift and nuclear
Overhauser effect data suggest that amino acids Q44-W49 near the C-terminus of
R2 form an unstable or nascent helix, which could be stabilised on binding to a
specific DNA target site. The two N-terminal helices in R2 and R3 occupy
essentially identical positions in the two domains, consistent with the high
level of sequence similarity between these regions. In contrast, the C-terminal
region forming the third helix in R3 shows low sequence similarity with R2,
accounting for the differences in secondary structure. In the case of B-MybR2R3,
there is a clear chemical shift and line-broadening evidence for the existence
of multiple conformations in the C-terminal region of R2, which is believed to
form one half of the DNA-binding site. We propose that conformational
instability of part of the DNA-binding motif is a way of increasing the
specificity of Myb proteins for a relatively short (6-bp) DNA target site by
reducing their affinity for non-specific DNA sequences compared to specific
sites.
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