FIG. 2.

Selection of substrates for ASLV integrase. Multiple rounds of selection by integration, amplification, and regeneration were carried out using ASLV integrase and substrates with terminal 5 in which the nucleotides were randomized (AL-5N) (A) or the 7 nucleotides adjacent to the conserved CA were randomized (AL-7NCA) (B). A sample of the reaction mixture of each round was sequenced, and lanes corresponding to termination reaction mixtures are shown. Round 0 is the sequence of the starting pool of double-stranded oligonucleotide substrates without any selection. The starting sequence is shown to the left of the gel, while specific nucleotide sequences emerging in the final round are shown to the right of the gel. The cycling was terminated when the substrate pool showed stronger-than-WT integration efficiency, as judged by the intensity of the integration-PCR product.