A Transcription Fidelity Reporter Identifies GreA as a Major RNA Proofreading Factor in .

We made a coupled genetic reporter that detects rare transcription misincorporation errors to measure RNA polymerase transcription fidelity in Using this reporter, we demonstrated that the transcript cleavage factor GreA, but not GreB, is essential for proofreading of a transcription error where a riboA has been misincorporated instead of a riboG. A mutant strain had more than a 100-fold increase in transcription errors relative to wild-type or a mutant. However, overexpression of GreB in Δ cells reduced the misincorporation errors to wild-type levels, demonstrating that GreB at high concentration could substitute for GreA in RNA proofreading activity .