Figure 1.

General mechanism of plasmid transfer. Conjugative plasmids carry an oriT and express proteins for pili, the envelope spanning T4 channel (Mpf), a T4CP (yellow), the secretion initiation complex (relaxosome), and secretion substrate and DNA nicking relaxase (pink). Some bifunctional relaxases are fused to a helicase or primase domain to facilitate conjugative DNA processing (dotted oval). T-DNA is processed as described in the text, and transferred as ssDNA. The complementary plasmid strand remains circular throughout. For simplicity, stages 1–4 of plasmid DNA processing are illustrated with linear DNA fragments.