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Tail Assembly and Injection

Isao Katsura


The tail of a bacteriophage is a supramolecular organelle with which the phage adsorbs to the host cell and injects its DNA into the cytoplasm. Only the relatively complex double-stranded DNA phages have a tail as a morphologically distinguishable, differentiated structure. The tails of these phages may be classified into three groups on the basis of morphology and function: long contractile (e.g., T4), long noncontractile (e.g., λ), and short (e.g., T7). In the long contractile and long noncontractile groups, tail assembly forms an independent branch in the morphogenetic pathway (Casjens and King 1975).

The assembly of the λ tail has been studied in detail. The results complement those of the T4 tail (King 1968) and give information useful to the studies of other tubular or helical structures, such as bacterial flagella (Iino 1977). Although the function of the λ tail itself may seem a very specialized field of research, problems contained in this study are more general: How do protein molecules function in assembled states where interaction between neighboring molecules is strong? How can we analyze a series of reactions occurring in such structures? The λ tail is a particularly advantageous model to use in attempting to understand the assembly and function of supramolecular structures due to the highly developed experimental approaches (genetic, structural, biochemical, immunological, and so on) available in this system.

The tail of phage λ is a thin flexible tube (135 nm in length), ending in a small conical part (15 nm in...

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