Analysis of decatenating activity in nuclear extracts from control (lanes 1 through 7) and RA-treated (lanes 8 through 14) HL-60 cells. The substrate 200 ng kDNA (TOPOGEN Inc) was incubated for 30 minutes with nuclear extracts that were serially diluted to contain the following: lanes 1 and 8 (1:2), lanes 2 and 9 (1:4), lanes 3 and 10 (1:8), lanes 4 and 11 (1:16), lanes 5 and 12 (1:32), lanes 6 and 13 (1:64), and lanes 7 and 14 (1:128). The position of the decatenated kDNA is indicated by the arrow.