Fig. 6.

Model for the interaction of DNA with the αHL pore. To pass through the pore (V), DNA must first collide with the cis entrance (II), be transported through the vestibule (III) and enter the β barrel (IV). The DNA can prolong its visit within the vestibule and produce midamplitude and low-amplitude events corresponding to VI and VII. All steps are reversible with exception of translocation. In type A events, DNA collides with the pore, enters the vestibule and then directly translocates through the β barrel to exit on the trans side. Sampling of the barrel (III → IV) during this process is too fast to observe. In type B events, DNA is captured by the pore but instead of penetrating the β barrel it has a prolonged interaction with the vestibule to produce the midamplitude event (I → II → III → VI). The DNA exits the pore from the cis entrance from which it entered (VI → III → II → I). Like type B events, type C events first show a midamplitude current (I → II → III → VI), but then one end of the DNA enters the β barrel (VII) and translocation occurs (VII → V → I). In type D events, the DNA enters the β barrel (I → II → III → IV) but then stops translocating (VII), retracts back into the vestibule (VI) and exits the pore from the cis side (VI → III → II → I). Finally, in type E events, the DNA begins to translocate as in type C events (I → II → III → VI → VII → V), but then retracts into the vestibule (V → VII → VI) and exits the pore from the cis side as in type D events (VI → III → II → I). Intermediates expected to give midamplitude events are numbered in yellow, although II and III would be too short for observation. Intermediates expected to give low-amplitude events are numbered in red, although IV would be too short for observation.