Transcription fidelity and its roles in the cell

Abstract

Accuracy of transcription is essential for productive gene expression, and the past decade has brought new understanding of the mechanisms ensuring transcription fidelity. The discovery of a new catalytic domain, the Trigger Loop, revealed that RNA polymerase can actively choose the correct substrates. Also, the intrinsic proofreading activity was found to proceed via a ribozyme-like mechanism, whereby the erroneous nucleoside triphosphate (NTP) helps its own excision. Factor-assisted proofreading was shown to proceed through an exchange of active centres, a unique phenomenon among proteinaceous enzymes. Furthermore, most recent in vivo studies have revised the roles of transcription accuracy and proofreading factors, as not only required for production of errorless RNAs, but also for prevention of frequent misincorporation-induced pausing that may cause conflicts with fellow RNA polymerases and the replication machinery.

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).