Inhibition by arsenic acid and reversal by ATP and GTP. Cells were treated by Method A with an incubation of 80 min. All compounds were added at the same time as thioredoxin. Tetracycline (20 μg/ml) was added to prevent residual protein synthesis. •, A307 (unc+); ○, K1640 (Δunc); □, K1640, 5 mM arsenic acid plus 10 mM ATP; ▵, K1640, 5mM arsenic acid plus 10 mM GTP.