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PDBsum entry 1nyh
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Transcription repressor
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PDB id
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1nyh
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References listed in PDB file
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Key reference
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Title
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Structure of the coiled-Coil dimerization motif of sir4 and its interaction with sir3.
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Authors
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J.F.Chang,
B.E.Hall,
J.C.Tanny,
D.Moazed,
D.Filman,
T.Ellenberger.
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Ref.
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Structure, 2003,
11,
637-649.
[DOI no: ]
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PubMed id
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Abstract
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The yeast silent information regulators Sir2, Sir3, and Sir4 physically interact
with one another to establish a transcriptionally silent state by forming
repressive chromatin structures. The Sir4 protein contains binding sites for
both Sir2 and Sir3, and these protein-protein interactions are required for gene
silencing. Here, we report the X-ray structure of the coiled-coil dimerization
motif within the C-terminus of Sir4 and show that it forms a stable 1:1 complex
with a dimeric fragment of Sir3 (residues 464-978). We have identified a cluster
of residues on the surface of the Sir4 coiled coil required for specific
interactions with Sir3. The histone deacetylase Sir2 can also bind to this
complex, forming a ternary complex with the truncated Sir3 and Sir4 proteins.
The dual interactions of Sir4 with Sir3 and Sir2 suggest a physical basis for
recruiting Sir3 to chromatin by virtue of its interactions with Sir4 and with
deacetylated histones in chromatin.
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Figure 5.
Figure 5. A Hydrophobic Patch of Residues on the Surface of
the Sir4 Coiled Coil Binds Sir3(A) A series of mutant Sir4-C2
proteins with amino acid substitutions at the exposed positions
along the length of the coiled coil were constructed and tested
for interaction with Sir3T by the GST pull-down assay with a 1:1
molar ratio of Sir3T and each Sir4-C2 mutant. Mutation of
residues M1307 and I1311 prevent binding to Sir3T, and mutation
of the neighboring residue E1310 strongly interferes with
binding to Sir3T.(B) The locations of the Sir4 residues that are
required for interaction with Sir3 are shown, colored as in
Figure 1B. The Sir3 binding site is present on each subunit of
the coiled-coil dimer, suggesting that two Sir3 molecules
interact with the Sir4 dimer (cf. Figure 6).(C) A series of
N-terminally truncated Sir3 proteins were tested for interaction
with the GST-Sir4-C2 coiled-coil domain. The Sir3 proteins were
expressed in E. coli and purified with a C-terminal His[6]
affinity tag prior to use in the pull-down experiment. The
efficiency of the interaction with Sir4-C2 is shown.(D)
Pull-down assays are shown that test the interaction of Sir4
with a series of N-terminally truncated Sir3 proteins. The
results show that the region of Sir3 between residues 495 and
522 is crucial for efficient binding to Sir4. This region is
exposed and proteolytically sensitive in the absence of Sir4
(see text for details).
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The above figure is
reprinted
by permission from Cell Press:
Structure
(2003,
11,
637-649)
copyright 2003.
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