FIG. 3.

Bias between IRs during IS911 circle formation. (A) Summary of the intramolecular transposition assay used to analyze bias between IRs during early steps of IS911 transposition. IRL and IRR are represented as two different arrows as in Fig. 2. The donor pAPT166 dimer plasmid, pAPT166₂, is illustrated. It carries two copies of IS911, each containing IRL and IRR with the endogenous promoter P_IRL partially located in IRL and an orfA-lacZ gene fusion. It also contains two copies of the pBR322 origin of replication (filled ovals) and two ampicillin resistance genes (not indicated). In vitro reaction with OrfAB (0.42 μM) generates the figure eight (inter-IS figure eight) which is processed after transformation into MC1061 recA, into an IS circle (IS tandem dimer). The IRL-IRR junction creates the P_junc promoter, which drives expression of the orfA-lacZ fusion. These colonies are red on MacConkey lactose indicator plates. Plasmid DNA isolated from individual lac⁺ clones was digested, and the fragment containing the junction was purified and sequenced. (B) Sequences of the IRL-IRR junctions. As expected, two types of junction sequences were obtained: the IRL-TGC-IRR junction corresponds to events in which IRL is used as the target, and the IRL-GAC-IRR junction is representative of events in which IRR is targeted by IRL.