Components	Volume per sample	Final amount/concentration
3′-end-labeled DNA	1 μl	~100,000 c.p.m.
10× drug concentration	2 μl	1×
10× Top1 reaction buffer (see REAGENT SETUP)	2 μl	1×
DTT (2 mM)	2 μl	0.2 mM
ddH2O	11 μl	—