Fig. 5.

Proposed transposition mechanism resulting in an inverted Ds and a flanking deletion at the site of excision. (A) The Ds element as present in the T-DNA context of the starter line. The donor locus has replicated, and the target site (TS) is located in unreplicated DNA. (B) Local transposition of one replicated Ds copy into the unreplicated TS produces a locally transposed Ds in inverted orientation. (C) Intermediate product with two closely linked Ds; only the relevant chromatid is shown. (D) The subsequent excision event involves the 5′ TIR of the newly transposed Ds and the 3′ TIR of the Ds at the donor locus. The hybrid element being excised contains plant genomic DNA Y, the left part of the T-DNA vector including the negative selectable marker IAAH, and the Ds element at the donor site. (E) The resulting deletion chromosome. The asterisk highlights the double-strand break repair signature between the T-DNA flanking the 3′ Ds end in the starter construct and the retained Ds. 5′ Ds TIRs are drawn in red, 3′ Ds TIRs in yellow, T-DNA in blue. X, Y, and Z indicate plant genomic DNA sequences. Arrowheads indicate DNA cuts by Ac transposase; arrows indicate the orientation of the Ds.