F-Pilus Insertion

The bacterial envelope contains a variety of pili, among which the F- provide the adsorption sites for two general classes of pilus-specific 

F-pili are rapidly synthesized from protein precursor molecules (pilin), which are localized in the inner membrane. The assembly and extrusion of the pili are mediated by an energy-requiring process. It has been shown 

More recently, we have obtained electron micrographs suggesting penetration of tubular pili through the outer membrane (Fig. 7). These observations suggest that the true anchoring site is at the plasma membrane. Plasma membrane anchoring of pili is also supported by the fact that the pili remained associated with spontaneously lysed cells, as well as to spheroplast preparations. 

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Fig. 6. Ultrathin section through E. coli HfrH, revealing the F-pilus insertion at the membrane adhesion zone. The pilus is labeled with bacteriophage MS2. (60,000x)...

Fig. 7. Sites of F-pilus insertion at adhesion zones. Left A lysing cell. Right The pilus seems to interrupt the profile of the outer membrane. (200,000x)...

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