Elucidating the Mechanisms Surrounding H2A.X Monoubiquitylation Marks in the DNA Damage Response Pathway

Abstract

In response to DNA double-strand breaks (DSBs), H2A.X undergoes three post-translational modifications (PTMs) reported to be important for DSB signaling: phosphorylation at serine 139, monoubiquitylation at lysines 118/119 and monoubiquitylation at lysines 13/15. We aimed to gain a better understanding of the mechanisms surrounding H2A.X monoubiquitylation marks and their relationship to H2A.X phosphorylation. We have developed and tested a novel purification method for the isolation of ubiquitylated H2A.X-containing nucleosomes, which can be used to co-purify DNA damage-response proteins that interact with ubiquitylated H2A.X-containing nucleosomes. Our data show that monoubiquitylation of lysines 118/119 is not required for phosphorylation at serine 139, nor for monoubiquitylation at lysines 13/15 in cis (on the same H2A.X molecule). Our data also suggests that monoubiquitylation of lysines 118/119 may have an antagonistic effect on monoubiquitylation of lysines 13/15. Lastly, we saw that different DSB-inducing agents can have different effects on H2A.X monoubiquitylation.