Fig. 5.

Force generation by cytoplasmic and outer membrane motors. (A) Hypothetical model for DNA transport through the Gram-negative cell envelope. A translocation ratchet drives uptake of DNA from the environment into the periplasm by reversible ComE binding. For transport across the inner membrane to occur, ComE must unbind. B. subtilis data suggest that in agreement with this prerequisite, the force generated by the cytoplasmic motor is considerably larger. (B) Reversal forces for B. subtilis (34), N. gonorrhoeae, and H. pylori (26). T4P/T2SS, type 4 pilus/type 2 secretion system; T4SS, type 4 secretion system.