F pili

Three types of thread-like appendages may be found growing from bacterial cells flagella, pili (fimbriae) and F-pili (sex strands). 

F-pili or sex strands are partofa primitive genetic exchange system in some bacterial species. Part of the genetic material may be passed from one cell to another through the hollow pilus, thus giving rise to a simple form of sexual reproduction. 

In addition to flagella, extremely thin, long, straight filaments known as pili or fimbriae (Fig. 1-2) project from the surfaces of many bacteria.14 The "sex pili" (F pili and I pili) of E. coli have a specific role in sexual conjugation. The similar but more numerous common pili or fimbriae range in thickness from 3 to 25 nm and in length from 0.2 to 2 pm. Pili are involved in adhesion of bacteria to surrounding materials or to other bacteria and facilitate bacterial infections.17-19 A typical E. coli cell has 100-300 pili.5... 

Other types of pili are also well-known.53 F pili or conjugative pili are essential for sexual transfer of DNA between bacterial cells (Chapter 26). F+ strains of E. coli form hollow pili of 8.5 nm diameter with a 2.0-nm central hole.58 59 Their 90-residue subunits apparently form rotationally symmetric pentamers which stack to form the pili.59 These pili are essential to establishing the initial contact between conjugating bacterial cells. 

To achieve surface display, five of the Ml3 coat proteins have been used in fusion to foreign protein fragments. In the most widespread system the antibody is coupled to the N-terminus or second domain of the minor coat protein pill (11,12,14). The naive function of the three to five copies of the pill, in particular their N-terminal domain, is to provide binding of the phage to the f-pili of E. coli to initiate infection (39). The major coat protein (pVIII) has been used as an alternative fusion partner, with only very few successes reported in the past decade (40). This fusion technique is more useful for the display of short peptides (41,42). Fusions to pVI have been tried, but not yet with antibodies (43). pVII and pIX were... 

E. coli F agent contains the genes needed to direct the synthesis of the F pili (sex pili). These tiny appendages, 8.5 nm in diameter (see Fig. 7-9), grow out quickly during a period of 4-5 min to a length of about... 

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... 

Pili. In addition to the F-pili, which have already been discussed, phage can also adsorb to I-pili. 

---