Histone H2A.X phosphorylation on Ser139 in response to DNA damage is the major signal for the assembly of the so-called gammaH2A.X chromatin domain, a region surrounding an unrepaired DNA double-strand break that is characterized by the accumulation of a large number of DNA damage response proteins. However, it is not yet clear how this event is regulated in space and time. The recent discovery of H2A.X Tyr142 phosphorylation by the WICH complex and its dephosphorylation by the EYA1/3 phosphatases may provide substantial novel insight into this process. WSTF, a subunit of the WICH complex bears a novel kinase domain at its N-terminus that constitutively targets H2A.X on Tyr142. This novel histone modification appears to determine the relative recruitment of either DNA repair or pro-apoptotic factors to sites of DNA damage. Thus, the balance of H2A.X Tyr142 phosphorylation/dephosphorylation may constitute a novel switch mechanism to determine cell fate after DNA damage.