Modifications of DNA-associated histone proteins maintain genome integrity. On damage to DNA, phosphorylation of histone H2A.X determines whether repair is justified or if the damaged cell must die.rnChromosomal DNA wraps around histone proteins to form a complex scaffold called chromatin. The reorganization of these proteins following DNA damage is crucial for repairing the damage, and so maintaining genomic integrity and reducing the likelihood of cell death or cancer. One such histone modification - known as γ-H2A.X - follows DNA double-strand breaks (DSBs) and involves phosphorylation by the enzyme ATM of serinernresidue 139, which is located in the carboxy-terminal tail of the histone variant H2A.X (ref. 2). γ-H2A.X generates a chromosomal microenvironment that promotes recruitment of repair proteins and facilitates DNA repair to reduce the risk of mutations. But how this modification is regulated and how it affects cell fate have remained elusive. Two papers, including one on page 591 of this issue, provide insights into these questions.
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