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Nat Struct Biol. 2000 Mar;7(3):209-14.

A closer view of the conformation of the Lac repressor bound to operator.

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  • 1The Johnson Foundation and Department of Biochemistry and Biophysics, University of Pennsylvania School of Medicine, 37th and Hamilton walk, Philadelphia, Pennsylvania 19102-6059, USA.


Crystal structures of the Lac repressor, with and without isopropyithiogalactoside (IPTG), and the repressor bound to operator have provided a model for how the binding of the inducer reduces the affinity of the repressor for the operator. However, because of the low resolution of the operator-bound structure (4.8 A), the model for the allosteric transition was presented in terms of structural elements rather than in terms of side chain interactions. Here we have constructed a dimeric Lac repressor and determined its structure at 2.6 A resolution in complex with a symmetric operator and the anti-inducer orthonitrophenylfucoside (ONPF). The structure enables the induced (IPTG-bound) and repressed (operator-bound) conformations of the repressor to be compared in atomic detail. An extensive network of interactions between the DNA-binding and core domains of the repressor suggests a possible mechanism for the allosteric transition.

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