Phosphorolytic error correction during transcription

Summary Escherichia coli DNA-directed RNA polymerase is shown to contain a novel phosphorolytic error correction activity which removes erroneous nucleotides, as rNDPs, from the 3′-end of the growing transcript. The activity we describe is biochemically similar to poly-nucleotide phosphorylase (PNP), yet in contrast to PNP is activated by Mn2+. We demonstrate that the activity, which is mediated by Pi, is dependent on the presence of an incorrectly incorporated nucleotide at the leading 3′-end of the transcript. The correction activity we describe exhibits a 4 × 104-fold preference for the excision of incorrect nucleotides from the transcript. These findings suggest the possibility that RNA phosphorolysis may play a critical role in the process of transcriptionai proofreading.