The prevailing view on post-translational modifications (PTMs) is that a single amino acid is modified with a single PTM at any given time. However, recent work has demonstrated crosstalk between different PTMs, some occurring on the same residue. Such interplay is seen with ADP-ribosylation and ubiquitylation. For example, DELTEX E3 ligases were reported to ubiquitylate a hydroxyl group on free NAD