Explain the means by which E.coli cell can encounter a promoter in the context of the genome.

There are four potential diffusion–based mechanisms that might contribute to the promoter search: (i) one–dimensional (1D) “hopping”, where the protein moves along the same molecule of DNA via a correlated series of submicroscopic dissociation and rebinding events before re–equilibrating back into free solution; (ii) 1D–sliding, where the protein executes a random walk along the DNA without dissociation; (iii) intersegmental transfer, where the protein moves from one site to another via a looped intermediate and (iv) three–dimensional diffusion (or “jumping”), where the protein starts out fully equilibrated with free solution (i.e. it has no memory of whether it has previously visited a DNA site) and then finds its targets through direct 3D–collisions from solution (Supplementary Fig. 1).