English: (A) (Left) Main components of an intrinsic terminator: a U-rich tract, and a GC-rich Thp structure. (Right) The Thp, by annealing an asRNA can create a GC-rich duplex. (B) The thermodynamic model for termination. The probability of each event is shown through relative free energy barriers to elongation (blue) versus termination (red). The stabilities of the RNA−DNA hybrid (pink) and RNAP−NA interactions (red) are proportional to the arrow height. (C) The steps of intrinsic termination. Red arrows show steps in termination; blue arrows show steps that bypass termination. RNA, red; DNA, black; RNAP, gray. (D) Elongation Complex structure (E) The TH and unfolded TL conformations. The spheres are points of mutations