Rpd3L Coordinates Chromatin State and Transcription-Replication Conflict Resolution through H3K4 Methylation-Dependent and Independent Mechanisms

Faithful genome duplication requires coordination between transcription and replication. Disruption of this coordination causes transcription-replication conflicts (TRCs), leading to replication stress and genome instability. How chromatin regulators modulate these processes remains unclear. Here, we show that the Rpd3L histone deacetylase complex dynamically modulates chromatin state to control replication fork progression and buffer TRCs in Saccharomyces cerevisiae. Rpd3L is targeted through both histone H3 lysine 4 methylation-dependent recruitment and methylation-independent mechanisms engaged under replication stress. Loss of H3K4 methylation or Rpd3L function promotes histone acetylation, accelerates fork progression through transcribed regions, and increases transcription-associated genome instability. Balanced acetylation at multiple histone lysines is required to stabilize replication forks under stress. While histone deacetylase complexes have been implicated in repairing damaged forks, our findings reveal that Rpd3L acts preemptively to modulate chromatin state and replication dynamics during TRCs, defining a chromatin-based mechanism that safeguards genome stability.