Figure 6.

T-DNA integration model based on micro-homologies between T-DNA and genomic DNA near the T-DNA RB (see also text). (A) Single-stranded T-DNA enters the nucleus covered with VirE2 protein (not shown) and with VirD2 attached to the 5′ end. (B) The 3′ end loops back and anneals to itself, thus providing a 3′-OH end to prime synthesis of a complementary T-DNA strand (broken line), thereby removing VirE2 (not shown). (C) T-DNA, still single stranded near the 5′ end, invades genomic DNA and finds a short stretch of micro-homology (vertical lines). Nicks will occur in the genomic DNA as indicated by the arrows. (D) The 3′ end loop in double-stranded T-DNA is degraded resulting in a left end deletion. Genomic DNA is degraded (thin broken lines), resulting in a target deletion. (E) VirD2 and the 5′ end of T-DNA upstream of the micro-homology is removed. Single-stranded gaps are repaired (arrows) and the DSB between the T-DNA left end and the genomic DNA is repaired, thereby generating filler DNA (short open bars).