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PDBsum entry 1mj2
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Transcription/DNA
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PDB id
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1mj2
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Contents |
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* Residue conservation analysis
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References listed in PDB file
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Key reference
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Title
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Direct and indirect readout in mutant met repressor-Operator complexes.
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Authors
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C.W.Garvie,
S.E.Phillips.
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Ref.
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Structure, 2000,
8,
905-914.
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PubMed id
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Abstract
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BACKGROUND: The methionine repressor, MetJ, represses the transcription of genes
involved in methionine biosynthesis by binding to arrays of two to five adjacent
copies of an eight base-pair 'metbox' sequence. Naturally occurring operators
differ from the consensus sequence to a greater extent as the number of metboxes
increases. MetJ, while accommodating this sequence variation in natural
operators, is very sensitive to particular base changes, even where bases are
not directly contacted in the crystal structure of a complex formed between the
repressor and consensus operator. RESULTS: Here we report the high-resolution
structure of a MetJ mutant, Q44K, bound to the consensus operator sequence
(Q44Kwt19) and two related sequences containing mutations at sites believed to
be important for indirect readout at non-contacted bases. The overall structure
of the Q44Kwt19 complex is very similar to the wild-type complex, but there are
small variations in sugar-phosphate backbone conformation and direct contacts to
the DNA bases. The mutant complexes show a mixture of direct and indirect
readout of sequence variations, with differences in direct contacts and DNA
conformation. CONCLUSIONS: Comparison of the wild-type and mutant
repressor-operator complexes shows that the repressor makes sufficiently strong
interactions with the sugar-phosphate backbone to accommodate some variation in
operator sequence with minor changes in direct bases contacts. The reduction in
repressor affinity for the two mutant repressor complexes can be partially
attributed to a loss in direct contacts to the DNA. In one case, however, the
replacement of a flexible TA base-step leads to an unfavourable DNA conformation
that reduces the stability of the repressor-operator complex.
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