#Id: 6308
#Unit 3. Fundamental Processes
RNA polymerase performs two proofreading functions on that growing transcript.
The first of these is called pyrophosphorolytic editing. In this, the enzyme uses its active site, in a simple back-reaction, to catalyze the removal of an incorrectly inserted ribonucleotide, by reincorporation of PPi. The enzyme can then incorporate another ribonucleotide in its place in the growing RNA chain. Note that the enzyme can remove either correct or incorrect bases in this manner, but spends longer hovering over mismatches than matches, and thus removes the former more frequently.
