Fig. 6

Proposed pathways of transposon circle formation together with replication and integration during Helraiser transposition. Transposon circle formation using the original donor site is shown on the left (I). Following the nicking of transposon plus strand at the LTS, a replication fork is established at the nick site (i). Leading strand synthesis reconstitutes the transposon donor site (ii), while lagging strand synthesis takes place on the displaced transposon strand. This results in a formation of dsDNA transposon circle (a′) after the second cleavage reaction takes place at the RTS of the displaced transposon strand. Generated dsDNA transposon circle potentially serves as a transposon donor (b′). Following the transposon plus-strand cleavage at the LTS-to-RTS junction site on a dsDNA transposon circle, a replication fork is established at the nick site (b′). Leading strand synthesis regenerates the transposon donor site on the transposon circle, while the lagging strand synthesis results in a dsDNA transposon copy that can be integrated in the host genome (c′) or form a new dsDNA transposon circle (d′). After resynthesis of the original transposon donor site (shown on the right (II)), transposon circle formation and replication include the same steps illustrated for the pathway (I). Solid line: original transposon donor strand; dashed line: synthesized transposon strand. Transposon plus strand is shown in dark purple or in dark green; transposon minus strand is shown in light purple or in light green. Red arrow marks the position of the transposon plus-strand cleavage at the LTS-to-RTS junction site