Co-transcriptional genome surveillance by HUSH is coupled to termination (RNA-Seq)

The HUSH complex recognizes and silences foreign DNA such as viruses, transposons, and transgenes without prior exposure to its targets. Recent studies revealed that HUSH recruitment is dependent on transcription, but a unifying molecular mechanism by which HUSH identifies its targets as ‘non-self’ DNA and selects them for silencing remains unknown. Harnessing a de novo silencing event in ESCs, we uncover distinct modes of HUSH function – one involves co-transcriptional surveillance in the absence of silencing, while the other is associated with H3K9me3 deposition and repression. We demonstrate that HUSH travels with elongating RNAPII, interacts with the transcriptional termination machinery, and accumulates on chromatin in a manner dependent on the termination factor WDR82. We further show that perturbation of endogenous termination signals triggers the switch from HUSH surveillance to silencing. Together, our results uncover an RNAi-independent, co-transcriptional gene silencing mechanism in mammals that senses aberrant termination to distinguish self from non-self. rRNA-depleted RNA-seq in R1 mouse embryonic stem cells