FIGURE 2.

The conjugative process. Conjugative plasmids encode all the elements necessary for conjugation, while mobilizable plasmids lack a cognate T4SS and most of them also lack the T4CP. The conjugative process can be divided into five main steps: (A) Assembly of the components. (B) Formation of the pre-initiation complex. The T4CP performs the reception of the relaxosome to the secretion channel. This interaction triggers the hexamerization of the T4CP, the ATP hydrolysis by T4CP and VirB11, and finally the activation of the secretion channel. Both conjugative and mobilizable plasmids employ the T4CP of a conjugative plasmid, except for the few mobilizable plasmids that encode their cognate T4CP. (C) Activation of the conjugative process and processing of the substrate. When the pilus recognizes a receptor bacterium, a signal is transmitted to the relaxosome and DNA is processed. Each relaxase accomplishes the processing of its cognate plasmid through the specific recognition of the oriT sequence. (D) Transfer of the substrate through the T4SS. This step is always accomplished via the T4SS encoded in the conjugative plasmid. The question mark indicates that many questions remain open. (E) Substrate reception and end of conjugation. Once the substrate enters the recipient bacterium, the ssDNA is recircularized and replicated. Color code: oriT, black; relaxase, red; T4CP, green; T4SS and pilus, blue; donor bacterium, orange; receptor bacterium, purple.