Figure 12. Effect of Lsr2 on Topoisomerase I Activity.

Different amounts of topoisomerase I were added to 200 ng of supercoiled ΦX174 RT DNA. Lanes 1, 5, and 9, no topoisomerase; lanes 2, 6, and 10, 2.4 units of topoisomerase; lanes 3, 7, and 11, 6 units of topoisomerase; lanes 4, 8, and 12, 12 units of topoisomerase. Lsr2 at 0.1 mg/ml or 0.4 mg/ml was added to the reaction either simultaneously with the topoisomerase or after 30 min incubation with topoisomerase alone. The reaction was then treated with 6% SDS and 4 mg/ml proteinase K analyzed on a 0.7% agarose gel and then stained with ethidium bromide.

(A) Topoisomerase I and Lsr2 were incubated simultaneously with ΦX174.

(B) Lsr2 was added 30 min after the topoisomerase incubation.

L, linearized plasmid; R, relaxed plasmid; S, supercoiled plasmid.