An amazing fact about DNA transcription is that the machinery not only copies DNA onto RNA, but checks it for errors. A story in ScienceDaily1 says that researchers would expect 100 times more errors statistically than the actual results of transcription in the cell.

One of the mechanisms revealed in more detail by researchers at University of Bristol and University of Leeds is a linear stalling process akin to an old-style typesetting machine. DNA “letters” are transcribed single-file by a machine called RNA polymerase.  When a wrong letter is inserted into the RNA transcript, the machine stalls and backs up. It then has a tiny “molecular scissors” that snips out the incorrect nucleotide and inserts the correct one.

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