Phosphorolytic error correction during transcription.

Escherichia coli DNA-directed RNA polymerase is shown to contain a novel phosphorolytrc 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 polynucleotide 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 x 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 transcriptional proofreading. [ABSTRACT FROM AUTHOR]