SPT6 functions in transcriptional pause-release via PAF1C recruitment [PRO-seq]

In vitro studies identified various factors including P-TEFb, SEC, SPT6, PAF1, DSIF, and NELF functioning at different stages of transcription elongation driven by RNA polymerase II (RNA Pol II). What remains unclear is how these factors cooperatively regulate pause/release and productive elongation in the context of living cells. Using an acute protein-depletion approach, we report that SPT6 depletion results in release of paused RNA Pol II. Short genes demonstrate a prominent release and a subsequent increase in mature transcripts, whereas long genes fail to yield mature transcripts due to a loss of processivity. Unexpectedly, the recruitment of PAF1 complex (PAF1C) to RNA Pol II fails upon SPT6 depletion, leading to the release of NELF-bound RNA Pol II into the gene bodies. Furthermore, SPT6 depletion impairs heat shock-induced pausing, pointing to a role for SPT6 in regulating RNA Pol II pause-release through PAF1C recruitment and NELF removal during the early elongation. Overall design: Examination of SPT6 functions in human cells using acute and rapid depletion system and high-throughput sequencing (ChIP-seq, RNA-seq, PRO-seq).