Active RNA polymerase (RNAP) somehow remains both stable and
mobile. In the 28 July Science Korzheva et al. combine the X-ray
crystal structure of Thermus aquaticus (Taq) core RNAP with
their own crosslinking data to derive a model of a functioning
bacterial core RNAP (Science 2000, 289:619-625). At the front, a
20° hinged movement closes the RNAP "jaws" around the downstream
DNA. At the back of the RNAP, the rudder region is positioned to
separate the exiting RNA from the DNA template strand.
Termination probably comes when an RNA hairpin disrupts
interactions with the rudder, triggering collapse of the
transcription bubble.