Cycloheximide-induced cells were treated with two chemical inhibitors of poly(ADP-ribose) polymerase. 3-Aminobenzamide inhibited 75% of PAP gene induction and 4-hydroxyquinazolone, the highly specific inhibitor of the enzyme, blocked almost completely PAP expression, suggesting that ADP-ribosylation was indeed required for the upregulation of PAP gene expression by cycloheximide