Figure 23-5: Morphogenetic pathway of bacteriophage SPP1. A, The first stable intermediate in phage assembly is the procapsid. It contains four proteins: major head protein G13P (grey shell), scaffolding protein G11P (small circles that fill the inner space of the structure), and the portal protein G6P associated with the minor head protein G7P localized at the portal vertex of the procapsid (white structure). The terminase complex (G1P-G2P) is represented by grey ovals and a white square. After interaction of the terminase-DNA complex with the portal vertex the DNA (thin line) is pumped into the head, the scaffolding protein is released, and capsid expansion occurs. Termination of DNA packaging requires headful cleavage of the DNA concatemer and release of the terminase-DNA concatemer from the portal vertex. The DNA-filled capsid is stabilized by binding of G15P and G16P to the portal vertex. Attachment to the portal vertex of the phage tail that is assembled in an independent assembly pathway completes SPP1 assembly. B, The micrograph shows stable assembly intermediates of the SPP1 morphogenetic pathway and its final product, the virion. pc: procapsid; fc: DNA-filled capsid; ip: infective phage. The bar represents 100 nm. Negative staining with uranyl acetate. (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 23-1, Figure 23-2, Figure 23-3, Figure 23-4, Figure 23-5, Figure 23-6, Figure 23-7, Figure 23-8

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