THE INITIATION OF BACTERIOPHAGE INFECTION 209 



sediment only the cells, and measuring the amount of the component that 

 remained unattached in the supernatant fluid. The amounts of ghost and 

 DNA components were determined by means of specific labeling with S^^ 

 and P^2, respectively, and the other components were detected in electron 

 micrographs. The results in Table I indicate that the site for attachment is 

 located on the fibers at the distal end of the phage tail. This conclusion is in 

 line with the earlier finding that phages T2, Tl, and T5 attached to cells by 

 the tip of the tail (Fig. 6 — Anderson, 1953; Weidel and Kellenberger, 1955), 



2. Killing of Bacteria 



Infection by a virulent phage such as T2 (see Chapter V, page 187) is invari- 

 ably lethal to a cell. The ability of T2 (and also T5) to kill cells (as measured 

 by the loss of colony -forming activity) does not depend on the production of 

 progeny phage; killing will also occur when phage multiplication has been 

 blocked by exposing the phage before infection to ultraviolet light or to 

 X-rays (Luria and Delbriick, 1942, Watson, 1950). Ghosts of T2, which are 

 devoid of DNA, also kill (Herriott, 1951). Attachment of a single ghost 

 particle is sufficient for this purpose and usually leads within a few minutes 

 to lysis of the cell (Herriott, 1951; French and Siminovitch, 1955; Herriott 

 and Barlow, 1957). Lysis also occurs rapidly when a large number of intact 

 phage attach to a smgle ceU (lysis-from-witJiout — Delbriick, 1940b). These 

 three methods of killing and lysing cells (with X-ray-inactivated phage or 

 with ghosts or by the process of lysis-from-ivithout) all appear to involve as a 

 first step the formation of cellular structures resembling protoplasts (see 

 Section III), which then lyse spontaneously (Watson, 1950; Visconti, 1953; 

 Zinder and Arndt, 1956). Protoplasts do not form in the course of productive 

 infection by a viable T2 particle (otherwise phage production could not occur 

 in the media usually used), which is an indication that an infected cell can 

 block the reaction between a phage coat and the cell surface that yield a 

 protoplast. 



The free tail rods found in crude lysates of T2 (Fig. 4) attach to cells but 

 do not kill (Kellenberger and Sechaud, 1957 — see Fig. 7). This fact suggests 

 that the phage component responsible for cell killing and lysis (under condi- 

 tions where there is no phage multiplication, as described in the preceding 

 paragraph) is located in the tail sheath. It may be the enzyme present in the 

 phage tail which degrades ceU wall material (see Section VII, B). 



3, Serology 



Two different antigenic components have been identified in T2, one located 

 in the tail and the other in the head of the coat (DeMars et al., 1953; Lanni 

 and Lanni, 1953). The tail contains the antigen specifying the production of 

 VOL. II — 14 



