ADP-ribosylation is the addition of one or more ADP-ribose moieties to a protein.[1][2] It is a reversible post-translational modification that is involved in many cellular processes, including cell signaling, DNA repair, gene regulation and apoptosis.[3][4] Improper ADP-ribosylation has been implicated in some forms of cancer.[5] It is also the basis for the toxicity of bacterial compounds such as cholera toxin, diphtheria toxin, and others.[6]