Gene expression can be regulated in many ways at the level of transcription or translation. The quickest way is to modify the gene product or protein. Post-translational modifications (PTMs) of proteins can alter their activity, interaction partners, complex affiliation, subcellular localization, or stability in response to changes in the cellular environment. There is a well-established and diverse range of PTMs. Phosphorylation is best characterized due to its essential role in a wide range of cellular processes such as the DNA damage response (DDR).