Figure 4.

Hypothetical model for T-DNA transfer from the bacteria into the plant cell. In the bacterial cell, the VirE1 chaperone prevents binding of VirE2 to ssDNA, as has been suggested (10–12), and possibly prevents VirE2-dependent channel formation in the bacterial membrane. VirE2 is transported through the VirB-VirD4 channel and subsequently inserts into the plant plasma membrane, allowing the transport of the ssDNA-VirD2 complex. The way in which the VirE2 molecules enter the cytoplasm is unclear. However, once in the cytoplasm, VirE2 protein molecules coat the complex, permitting its transfer to the nucleus (1–3). For simplicity, the pilus and its involvement in T-DNA transfer are omitted from the scheme.