Phosphorylated H2A.X is a critical chromatin marker of DNA damage repair (DDR) in higher eukaryotes. However, H2A.X gene expression remains relatively uncharacterised. Replication-dependent (RD) histone genes generate poly(A)- mRNA encoding new histones to package DNA during replication. In contrast, replication-independent (RI) histone genes synthesise poly(A)+ mRNA throughout the cell cycle, translated into histone variants that confer specific epigenetic patterns on chromatin. Remarkably H2AFX, encoding H2A.X, is a hybrid histone gene, generating both poly(A)+ and poly(A)- mRNA isoforms. Here we report that the selective removal of either mRNA isoform reveals different effects in different cell types. In some cells, RD H2A.X poly(A)- mRNA generates sufficient histone for deposition onto DDR associated chromatin. In contrast, cells making predominantly poly(A)+ mRNA require this isoform for de novo H2A.X synthesis, required for efficient DDR. This highlights the importance of differential H2A.X mRNA 3’-end processing in the maintenance of effective DDR.

磷酸化的H2A.X是高级真核生物中DNA损伤修复（DDR）的关键染色质标记。但是，H2A.X基因表达仍然相对不为人所知。复制依赖性（RD）组蛋白基因在复制过程中产生编码新组蛋白的poly（A）-mRNA，以包装DNA。相反，复制非依赖性（RI）组蛋白基因在整个细胞周期内合成poly（A）+ mRNA，翻译成组蛋白变体，赋予染色质特定的表观遗传模式。显着的H2AFX编码H2A.X的是一种杂种组蛋白基因，可同时产生poly（A）+和poly（A）-mRNA同工型。在这里，我们报告选择性去除任一mRNA同工型揭示了不同细胞类型中的不同作用。在某些细胞中，RD H2A.X poly（A）-mRNA产生足够的组蛋白，以沉积到DDR相关的染色质上。相反，主要产生poly（A）+ mRNA的细胞需要这种同工型才能从头合成H2A.X，这是有效DDR所需的。这突出了差异H2A.X mRNA 3'末端加工在维持有效DDR中的重要性。