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PDBsum entry 1tlh
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Transcription
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PDB id
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1tlh
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References listed in PDB file
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Key reference
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Title
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T4 asia blocks DNA recognition by remodeling sigma70 region 4.
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Authors
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L.J.Lambert,
Y.Wei,
V.Schirf,
B.Demeler,
M.H.Werner.
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Ref.
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EMBO J, 2004,
23,
2952-2962.
[DOI no: ]
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PubMed id
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Abstract
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Bacteriophage T4 AsiA is a versatile transcription factor capable of inhibiting
host gene expression as an 'anti-sigma' factor while simultaneously promoting
gene-specific expression of T4 middle genes in conjunction with T4 MotA. To
accomplish this task, AsiA engages conserved region 4 of Eschericia coli
sigma70, blocking recognition of most host promoters by sequestering the
DNA-binding surface at the AsiA/sigma70 interface. The three-dimensional
structure of an AsiA/region 4 complex reveals that the C-terminal alpha helix of
region 4 is unstructured, while four other helices adopt a completely different
conformation relative to the canonical structure of unbound region 4. That AsiA
induces, rather than merely stabilizes, this rearrangement can be realized by
comparison to the homologous structures of region 4 solved in a variety of
contexts, including the structure of Thermotoga maritima sigmaA region 4
described herein. AsiA simultaneously occupies the surface of region 4 that
ordinarily contacts core RNA polymerase (RNAP), suggesting that an AsiA-bound
sigma70 may also undergo conformational changes in the context of the RNAP
holoenzyme.
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Figure 2.
Figure 2 Three-dimensional structure of T. maritima  A
SR4. (A) Superposition of the NMR structure family. Chemical
shifts for residues 379 -383 (the loop between S4 and S5) were
not identified and this segment is relatively disordered in the
family. (B) Helix arrangement in TmSR4. Helix S1 (residues 322
-329), helix S2 (residues 334 -342), helix S3 (residues 353
-361), helix S4 (residues 364 -377) and helix S5 (residues 385
-393) were identified from secondary 13C[  /
 ]shifts,
d[NN] (i, i+1) NOEs and 3J[NH ]coupling
constants. (C) Hydrophobic core of TmSR4 formed from nonpolar
residues found in all the five helices. (D) Superposition of
TmSR4 (blue), the T. aquaticus A
SR4 in its DNA-bound conformation (red) (Campbell et al, 2002)
and the T. thermophilus A
SR4 in its holoenzyme conformation (green) (Vassylyev et al,
2002).
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Figure 6.
Figure 6 AsiA remodels the conformation of SR4. The structure of
TmSR4 (blue) is compared to the structure of AsiA-bound EcSR4
(green) in two views. The C-termini of helices S1 -S4 are
colored red. Helix S5 seen in TmSR4 is unfolded in EcSR4 and the
unfolded segment has been excluded from the views of EcSR4 for
clarity. (A) Lateral view along helix S4 and (B) top view
rotated 90° about the horizontal axis relative to (A). Apparent
in both views, helix S2 in the complex is inverted
N-to-C-terminus and helix S1 is repositioned by approximately
180° in the AsiA-bound conformation relative to the conformation
in TmSR4. The DNA-binding HTH element (helices S3 and S4) is
unfolded from its canonical orientation in TmSR4 and forms a
pseudo-continuous helix in the AsiA-bound state.
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The above figures are
reprinted
from an Open Access publication published by Macmillan Publishers Ltd:
EMBO J
(2004,
23,
2952-2962)
copyright 2004.
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