Figure 4.
Proposed kinetic mechanism for transcription termination at the his terminator. E, RNAP; D, DNA template; R, RNA transcript. Subscripts n−1, n, or n+1 indicate the length of the transcript in nucleotides, with the terminated transcript having length n. States marked with asterisks (*) are normal intermediates in the elongation reaction; E-D-Rn represents the paused state. For simplicity, the multiple step transcript elongation cycles (11) are shown as single steps with apparent first-order rate constants kn−1 and kn equal to 4.8 s−1. Reaction steps are shown as irreversible when at least one product produced by the step is at negligible concentration in the experiments.