Figure 12-5: A hypothetical model for assembly and extrusion of filamentous phage. Initiation of phage assembly occurs when a cytoplasmic region of pI recognizes the packaging signal (PS), which protrudes from one end of the pV-ssDNA complex. Assembly occurs at sites where the cytoplasmic and outer membranes are brought together by trans-envelope interactions between pI and pXI in the cytoplasmic membrane and pIV in the outer membrane. Assembly starts with the addition of 3-5 copies each of two small 'tip' proteins (pVII and pIX). During elongation, which requires host thioredoxin (TrxA) and ATP hydrolysis (presumably by pI), pV is stripped from the DNA and several thousand copies of the major coat protein, pVIII, are added to form the phage tube, which surrounds the ssDNA. When the end of the DNA has been reached, pIII and pVI are added, and a conformational change in pIII detaches them from the membrane, thereby releasing the completed phage, which is extruded through the pIV channel. (for better image quality, click here for tif image, which may be quite large; may also require screen refreshing plus special software to view; or view larger tif in separate window)

Figure 12-1, Figure 12-2, Figure 12-3, Figure 12-4, Figure 12-5, Figure 12-6

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