Enzymatic activity of representative IN proteins. Increasing amounts of recombinant IN were incubated in the presence of oligonucleotide substrates for 1 h at 37°C in triplicate reactions. The products were separated by denaturing PAGE. (A) dBY-1 disintegration substrate is comprised of viral DNA and target DNA components which, upon addition of IN, are resolved to their respective parts. Gels from disintegration assays are shown for (B) reference IN and (C) IN containing K156R. (D) V1-V2, the 21-mer corresponding to the viral LTR, undergoes 3′-end processing and strand transfer in the presence of IN. (E) Reference IN; (F) IN containing K156R. The numbers at the top of each lane indicate the enzyme concentration (nM); S, substrate control; *, substrate; →, disintegration product; −2→, 3′-end processing product; S.T.P., strand transfer products.