Transcription elongation factor S‐II maintains transcriptional fidelity and confers oxidative stress resistance

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Abstract
Background: During transcription elongation, RNA polymerase II is arrested on the template when incorrect ribonucleotides are incorporated into the nascent transcripts. Transcription factor S‐II enhances the excision of these mis‐incorporated nucleotides by RNA polymerase II and stimulates transcription elongation in vitro. This mechanism is considered to be transcriptional proof‐reading, but its physiological relevance remains unknown. Results: We report that S‐II contributes to the maintenance of transcriptional fidelity in vivo. We employed a genetic reporter assay utilizing a mutated lacZ gene from which active β‐galactosidase protein is expressed when mRNA proof‐reading is compromised. In S‐II‐disrupted mutant yeasts, β‐galactosidase activity was ninefold higher than that in wild‐type. The S‐II mutant exhibited sensitivity to oxidants, which was suppressed by introduction of the S‐II gene. The mutant S‐II proteins, which are unable to stimulate transcription by RNA polymerase II in vitro, did not suppress the sensitivity of the mutants to oxidative stress or maintain transcriptional fidelity. Conclusion: These results suggest that S‐II confers oxidative stress resistance by providing an mRNA proof‐reading mechanism during transcription elongation.