Polymerase pausing induced by sequence-specific RNA binding protein drives heterochromatin assembly

摘要: Packaging of pericentromeric DNA into heterochromatin is crucial for genome stability, development and health, yet its endogenous triggers remain poorly understood. A defining feature histone H3 lysine 9 methylation (H3K9me). In S. pombe, transcripts derived from the dg dh repeat during S phase promote formation through two pathways: an RNAi-dependent mechanism involving recruitment Clr4 H3K9 methyltransferase complex (CLR-C) via RITS complex, RNAi-independent RNAPII-associated RNA-binding protein Seb1, repressor SHREC, RNA processing activities. We show here that Seb1 promotes long-lived RNAPII pausing. Pause sites associated with sequence-specific binding events are significantly enriched in regions their presence correlates heterochromatin-triggering activities corresponding fragments. Remarkably, globally increasing stalling by other means induces novel large ectopic domains. Such occurs even cells lacking functional RITS, demonstrating pausing can be sufficient to trigger de novo independently RNAi. These results uncover Seb1-mediated polymerase as a new signal nucleating assembly repetitive DNA.