DNA Damage-Induced Phosphorylation of Histone H2A at Serine 15 Is Linked to DNA End Resection

Abstract

The repair of DNA double-strand breaks (DSBs) occurs in chromatin and several histone post-translational modifications have been implicated in the process. Modifications of histone H2A N-terminal tail has also been linked to DNA damage response, through acetylation or ubiquitination of lysine residues that regulate repair pathway choice. Here, we characterize a new DNA damage-induced phosphorylation on chromatin, at serine 15 of H2A in yeast. We show that this SQ motif functions independently of the classical S129 C-terminal site (γH2A) and mutant mimicking constitutive phosphorylation increases cell sensitivity to DNA damage. H2AS129ph is induced by Tel1^ATM and Mec1^ATR, and loss of Lcd1^ATRIP or Mec1 signaling decreases γH2A spreading distal to the DSB. In contrast, H2AS15ph is completely dependent on Lcd1^ATRIP, indicating that this modification only happens when end resection is engaged. This is supported by an increase of RPA and a decrease in DNA signal near the DSB in the H2AS-15E phosphomimic mutant, indicating higher resection. This serine is replaced by a lysine in mammals (H2AK15), which undergoes an acetyl-monoubiquityl switch to regulate binding of 53BP1 and resection. This regulation seems functionally conserved with budding yeast H2AS15 and 53BP1-homolog Rad9, using different post-translational modifications between organisms but achieving the same function.