Operator regions repressor recognition

Figure 8.15 Sequence-specific protein-DNA interactions provide a general recognition signal for operator regions in 434 bacteriophage, (a) In this complex between 434 repressor fragment and a synthetic DNA there are two glutamine residues (28 and 29) at the beginning of the recognition helix in the helix-turn-helix motif that provide such interactions with the first three base pairs of the operator region.

Hence the specific interactions between two macromolecules essential for life, antibodies and nucleic acids, could represent, at the molecular level, a model of recognition as unique as that of the interaction between a repressor and the region of the genome corresponding to the operator, or the interaction between a tRNA and its appropriate synthetase. 

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