Brownian ratchet mechanism of translocation in T7 RNA polymerase facilitated by a post-translocation energy bias arising from the conformational change of the enzyme
(color online) T7 RNAP translocation-elongation cycle. (a) A substrate insertion complex (PDB 1S76) with the fingers domain in closed conformation and residue Tyr639 away from the active site (referred to as PRE position). The template nucleotide to be transcribed is numbered i + 1. The NTP binding site (active site) is shown in a red oval. (b) A pre-translocation complex (PDB 1S77) with the fingers domain in closed conformation and residue Tyr639 in PRE position. (c) A post-translocation complex (PDB 1H38) with the fingers domain in open conformation and residue Tyr639 close to the active site (referred to as POST position). (d) A pre-insertion complex (PDB 1S0V) with the fingers domain in open conformation and residue Tyr639 in POST position.
