Figure 4.

Competition between L-731,988 and target DNA substrates in strand transfer. (A) Effect of target concentration on inhibition. In a staged microtiter plate assay (18), integrase was assembled on donor DNA and washed. After assembly, the reactions were incubated with L-731,988 (0–0.4 μM) and a titration of target DNA ranging from 0 to 125 nM. The effect of increasing amounts of target DNA on the IC₅₀ for the inhibition of strand transfer by L-731,988 is shown. (B) The effect of target preincubation on inhibition. Integrase was assembled on donor DNA in the presence of MnCl₂. Unbound integrase and MnCl₂ were removed, and target DNA was added in the absence of divalent cation. Target DNA was incubated for 0–30 min. At the specified time, L-731,988 was titrated into the reactions, and strand transfer was initiated with MnCl₂. The IC₅₀ for the inhibition of strand transfer activity by L-731,988 as a function of time of preincubation with the target is shown.