The dynamic network of IS30 transposition pathways
Fig 1
Schematic model of IS30 transposition.
(A) Molecular model of the formation of IS minicircles and IS-dimers (IS30)2. The IS element is delimited by open (IRL) and filled (IRR) triangles representing the 26-bp left and right inverted repeats, respectively. The two bases adjacent to the Tpase-generated nick next to the donor end are indicated by open circles. The two bases bordering the targeted end at the same strand are shown as filled circles. The free 3’OH ends (3’) are indicated. Note that the same reaction produces a Tn-circle that is formally equivalent to the (IS30)2 dimer, if the IRs of two IS30 copies are joined. (B) A mechanistic model of the two-step copy-out-paste-in transposition of IS30. The IS elements are shown as open boxes delimited by IRL and IRR. Thin line, donor replicon; thick line, target replicon. Solid and dashed arrows indicate transposition and non-transposition events, respectively. Dimer replicon may arise by homologous recombination. Letters show the order of genes and indicate inversion or deletion on the donor replicon (intramolecular transposition). One of the deletion products is not detectable if it cannot replicate (crossed). IS minicircle is frequently produced from a dimer via DDS, but any IS copy can also produce circular element via a SSD-like process.