Fast ribozyme cleavage releases transcripts from RNA polymerase II and aborts co-transcriptional pre-mRNA processing

摘要

We investigated whether a continuous transcript is necessary for co-transcriptional pre-mRNA processing. Cutting an intronwith the fast-cleaving hepatitis S ribozyme, but not the slower hammerhead, inhibited splicing. Therefore, exon tethering toRNA polymerase II (Pol II) cannot rescue splicing of a transcript severed by a ribozyme that cleaves rapidly relative to the rateof splicing. Ribozyme cutting also released cap-binding complex (CBC) from the gene, suggesting that exon 1 is not tethered.Unexpectedly, cutting within exons inhibited splicing of distal introns, where exon definition is not affected, probably owing todisruption of the interactions with the CBC and the Pol II C-terminal domain that facilitate splicing. Ribozyme cutting withinthe mRNA also inhibited 3' processing and transcription termination. We propose that damaging the nascent transcript abortspre-mRNA processing and that this mechanism may help to prevent association of processing factors with Pol II that is notproductively engaged in transcription.