Figure 2. Transposition Is Targeted to Structures, Not Sequences.

(A) Depiction of two plasmids encoding inverted repeats, identical in sequence. One plasmid stably maintains a linear inverted repeat; the other forms a stable cruciform, with two extruded hairpin arms.

(B) Transposition is stimulated by cruciform structures. Single insertion (nicked plasmid) and double insertion (linearized plasmid) transposition products formed from three inverted repeat targets in linear or cruciform conformation were resolved on a 1% native agarose gel. Results shown here are representative of three independent experiments; similar data were obtained with a second RAG protein preparation.

(C) ScaI digestion of plasmids after transposition yields two distinct products when transposition is targeted to a specific part of the plasmid. A plasmid lacking cruciforms is used for illustration.

(D) Plasmid-encoded inverted repeats target transposition only when a cruciform is extruded. After digestion with ScaI, transposition products were separated on a 1% alkaline agarose gel.

C, cruciform; D, double insertion product; E, expected sizes of digested products if transposition was targeted to cruciform; L, linear inverted repeat; S, single insertion product; SE, signal ends; U, undigested transposition products.