Allostery is well documented for proteins but less recognized for DNA-protein interactions. Here, we report that specific binding of a protein on DNA is substantially stabilized or destabilized by another protein bound nearby. The ternary complex's free energy oscillates as a function of the separation between the two proteins with a periodicity of ∼10 base pairs, the helical pitch of B-form DNA, and a decay length of ∼15 base pairs. The binding affinity of a protein near a DNA hairpin is similarly dependent on their separation, which - together with molecular dynamics simulations - suggests that deformation of the double-helical structure is the origin of DNA allostery. The physiological relevance of this phenomenon is illustrated by its effect on gene expression in live bacteria and on a transcription factor's affinity near nucleosomes.
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