mRNA Decapping Factors and the Exonuclease Xrn2 Function in Widespread Premature Termination of RNA Polymerase II Transcription

We report a function of human mRNA decapping factors in control of transcription by RNA polymerase II. Decapping proteins Edc3, Dcp1a, and Dcp2 and the termination factor TTF2 coimmunoprecipitate with Xrn2, the nuclear 5'-3' exonuclease torpedo that facilitates transcription termination at the 3' ends of genes. Dcp1a, Xrn2, and TTF2 localize near transcription start sites (TSSs) by ChIP-seq. At genes with 5' peaks of paused pol II, knockdown of decapping or termination factors Xrn2 and TTF2 shifted polymerase away from the TSS toward upstream and downstream distal positions. This redistribution of pol II is similar in magnitude to that caused by depletion of the elongation factor Spt5. We propose that coupled decapping of nascent transcripts and premature termination by the torpedo mechanism is a widespread mechanism that limits bidirectional pol II elongation. Regulated cotranscriptional decapping near promoter-proximal pause sites followed by premature termination could control productive pol II elongation.