Fig. 2.

The elongation complex and models of RNA release in termination. (A) A model of an elongation complex showing helix rotation that would accompany branch migration in mechanical models of termination. (B) Termination by forward translocation. (C) Termination by bubble collapse. A shows a particular intrinsic transcription terminator poised at the site of release, but B and C are general to both intrinsic and enzymatic termination. The upstream rewound segment is indicated by the blue overscreen.