ADP-ribosylation of poly-L-arginine. Recombinant chicken ART4 (0.7 μg) was incubated in 100 μl PBS containing 1 mM ADP-ribose, 50 μM [32P]-NAD+ (10 μCi/assay) in the presence or absence of poly-L-arginine (1 mg/ml) for 30 min at 37°C. After incubation the samples were precipitated and collected on Whatman glass-fibre filters as described in the materials and methods. Incorporated radioactivity was measured by liquid scintillation counting. Data show the mean ± S.D. (n = 3).