探討組蛋白修飾調節RNA轉錄-DNA複製衝突之機制

Abstract

RNA轉錄與DNA複製衝突（TRCs）好發於活躍的轉錄基因組上。此過程不僅影響DNA複製叉的穩定性，也有可能造成基因突變。因RNA轉錄過程而產生的甲基化H3K4（H3K4me）組蛋白標記所在位置與TRCs熱區有一定關聯性，但是它們之間的相互作用尚且未知。本實驗發現H3K4me標記會加劇DNA複製期細胞週期檢查點缺失細胞內所發生的TRCs所導致的DNA複製機制之失能，並且發現該組蛋白標記具有減緩DNA複製叉的前進速率。細胞在應對DNA複製壓力時，完整的DNA複製期細胞週期檢查點功能與H3K4me是必要的，在TRCs發生頻率最高，且H3K4me被標記最多之高度表現的基因區域更顯得尤其重要。H3K4me透過降低DNA複製叉前進速率以緩解TRCs遭遇之強度，與在路況複雜的公路上設置減速丘迫使行進中的車輛將速度放緩以降低意外發生的機率如出一轍。此研究在活躍基因區域為何會被標記H3K4me的謎題上提出了新觀點，即此標記係細胞用以應對因TRCs所造成DNA複製壓力致基因不穩定之緩衝機制。

Transcription-replication conflicts (TRCs) occur when intensive transcriptional activity compromises replication fork stability, potentially leading to gene mutations. Transcription-deposited H3K4 methylation (H3K4me) is associated with regions that are susceptible to TRCs; however, the interplay between H3K4me and TRCs is unknown. Here we show that H3K4me aggravates TRC-induced replication failure in checkpoint-defective cells, and the presence of methylated H3K4 slows down ongoing replication. Both S-phase checkpoint activity and H3K4me are crucial for faithful DNA synthesis under replication stress, especially in highly transcribed regions where the presence of H3K4me is highest and TRCs most often occur. H3K4me mitigates TRCs by decelerating ongoing replication, analogous to how speed bumps slow down cars. These findings establish the novel concept that H3K4me defines the transcriptional status of a genomic region and defends the genome from TRC-mediated replication stress and instability.