Mediator-associated proteins and the small RNA-guided Polycomb repressive complex enhance cryptic transcription for transposon exclusion.

Cryptic transcription driven by Mediator complex proteins Dima1 and Emit2 promotes transposon exclusion in Tetrahymena, with disruption causing genome instability.

• Why it matters: Maintaining genome integrity requires effective suppression of transposable elements (TEs), but the mechanisms generating TE-specific regulatory RNAs and preventing TE activity remain unclear.
• What they did: The study used molecular and genetic approaches to show that cryptic transcription from outside canonical promoters depends on Mediator complex-associated proteins Dima1 and Emit2, and that sRNA-guided Polycomb recruitment reinforces this process in Tetrahymena.
• The result: Disruption of Dima1 abolishes cryptic transcription, causes accumulation of non-TE sRNAs, and leads to erroneous genome elimination and cell death, highlighting a regulatory circuit that ensures TE exclusion and genome stability.