FIG. 15.

Speculative model for Tol-dependent filamentous phage DNA translocation. The model is depicted in six consecutive stages. In stage 1, the filamentous bacteriophage contacts the bacterial cell and binds to the tip of an F pilus by its reception N2 domain (r). In stage 2, the interaction between g3p-N2 and the F pilus dissociates g3p-N1. In stage 3, the F pilus retracts and brings the g3p molecule into the periplasm, where it interacts through the translocation domain (t) with the TolA C-terminal domain (TolAIII). In stage 4, the g3p-N2 domain interacts with the TolA central domain (TolAII). In stage 5, the g3p-N3 domain that anchors the minor coat protein into the phage particle dissociates, inserts into the inner membrane, oligomerizes, and forms pores by which the single-stranded DNA (in red) translocates (stage 6) after disaggregation of the capsid by the insertion of the major coat g8p proteins into the membrane. The TolA degradation product observed upon the treatment of WT cells with M13 bacteriophage is represented (A*). Periplasm is on the top, and cytoplasm is on the bottom. The insert at stage 2 represents the electron microscopy picture of an M13 filamentous bacteriophage bound at an F pilus tip (bar, 100 nm). (Reprinted from reference 442 with permission.)