ADP-ribosylation of cysteine in prostate cancer cells, wheremodification occurs with mono-ADP-ribose (MAR), was recently shownto be a critical feature of a gene expression mechanism involvingthe androgen receptor (AR), a ligand-regulated transcription factor.12 Androgen binding to the ligand binding domain(LBD) of AR induces a conformational change of the unstructured N-terminaldomain (NTD), enabling its interaction with the LBD. Here, AR is linked to prostate cancer.