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Title
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NMR assignments for the amino-terminal residues of trp repressor and their role in DNA binding.
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Authors
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C.H.Arrowsmith,
J.Carey,
L.Treat-Clemons,
O.Jardetzky.
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Ref.
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Biochemistry, 1989,
28,
3875-3879.
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PubMed id
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Abstract
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The trp repressor of Escherichia coli specifically binds to operator DNAs in
three operons involved in tryptophan metabolism. The NMR spectra of repressor
and a chymotryptic fragment lacking the six amino-terminal residues are
compared. Two-dimensional J-correlated spectra of the two forms of the protein
are superimposable except for cross-peaks that are associated with the
N-terminal region. The chemical shifts and relaxation behavior of the N-terminal
resonances suggest mobile "arms". Spin-echo experiments on a ternary complex of
repressor with L-tryptophan and operator DNA indicate that the termini are also
disordered in the complex, although removal of the arms reduces the DNA binding
energy. Relaxation measurements on the armless protein show increased mobility
for several residues, probably due to helix fraying in the newly exposed
N-terminal region. DNA binding by the armless protein does not reduce the
mobility of these residues. Thus, it appears that the arms serve to stabilize
the N-terminal helix but that this structural role does not explain their
contribution to the DNA binding energy. These results suggest that the
promiscuous DNA binding by the arms seen in the X-ray crystal structure is found
in solution as well.
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