Many gene regulatory motifs in both prokaryotes and eukaryotes involve physical manipulations of the genetic material, often on length scales short enough that the mechanical properties of the DNA significantly impact gene expression. One class of such manipulations, called “action at a distance”, includes transcription factor-mediated DNA looping, in which a binding site some distance away on the DNA is brought into close proximity with the transcription machinery at the promoter. DNA looping is a...