Figure 1.

Multistep processes ensuring transcription fidelity. A schematic representation of the active centre of RNAP is given for different transcription intermediates, and shows template DNA and RNA (black lines), metal ions (red circles), the i + 1 site (grey oval) and the Trigger Loop (orange ribbon). Correct and incorrect incoming NTPs are coloured in black and blue, respectively. Green arrows show the direction of reactions leading to a correct transcript. The different thickness of the arrows serves only as a qualitative indication of the rates of reactions or conformational changes. At the bottom of the figure, a cartoon depicts a stalled misincorporated elongation complex, which may potentially cause transcription traffic jams with trailing RNAPs (left), and conflicts with replication forks (right).