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.