Single-molecule dynamics of transcription of the lar promoter.

We measured the in vivo production of RNA molecules tagged with MS2d-GFP in Escherichia coli, driven by the lar promoter, under weak and medium induction. The distributions of intervals between consecutive productions of RNAs are found to be sub-exponential, and the process of RNA production is found to be sub-Poissonian. We discuss possible models of transcription initiation and, based on our results and previous in vitro measurements, find that a sequential two-step model of transcription initiation at the promoter region explains the results well.