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  • Title: Mechanism of Lac repressor switch-off: orientation of the Lac repressor DNA-binding domain is reversed upon inducer binding.
    Author: Kamashev DE, Esipova NG, Ebralidse KK, Mirzabekov AD.
    Journal: FEBS Lett; 1995 Nov 13; 375(1-2):27-30. PubMed ID: 7498473.
    Abstract:
    Lac repressor's DNA-binding domains contain helix-turn-helix motif which, though similar to those of phage lambda Cro protein, are oriented differently with respect to DNA: in the specific complexes with Lac operator, N termini of the repressor's subunits are facing inwards. We demonstrate that, in the presence of an inducer, the repressor's N termini cross-link to the operator's outermost nucleotides. We suggest that the inducer fixes the repressor's DNA-binding domains in the Cro-type configuration and thus garbles its recognition surface. Since the Cro-type configuration is perfectly suitable for binding the DNA, this also explains how the switched-off repressor retains its non-specific DNA-binding.
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