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transcription_factors-3 - MetJ binds DNA with...

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MetJ binds DNA with a β -ribbon-helix-helix motif Direct readout provided by H-bonds between amino acid side chains of the β -sheets and the edges of bases in major groove. Indirect readout with a phosphate of the backbone, as sequence of operator results in “overtwist” in the complex and a bulged phosphate. The helices are involved in indirect readout. SAM co-repressor effects: No major allosteric alteration of the protein. The charge of SAM is required for its co-repressor activity. Long-range electrostatic interactions with the sugar-phosphate backbone. This arrangement is called an “electric-genetic switch”.
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Comparison of zinc finger modules to other types of DNA-binding motifs In HTH and β -ribbon-helix-helix proteins, a fairly substantial domain is required to enclose thehydrophobic core of the DNA-binding element. Binding is restricted to symmetric sites. In zinc finger proteins, zinc ions are used to coordinate a very small globular domain.
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