t2 and other bacterial viruses 465 



one finds that the lytic activity has been greatly increased and that with T4 

 tryptophan is no longer required. Further, if one studies the interaction be- 

 tween T2 and cell walls prepared from strain E. coli B/2, which is not at- 

 tacked by T2, it is found that while the cell membranes are not attacked by 

 the intact T2 virus, the usual lytic process does occur with the modified 

 particle obtained after removal of the distal portion of the tail. All of these 

 experiments indicate that removal of the distal portion of the viral tail ex- 

 poses an area capable of lytic activity. Recently Koch and Jordan (1957) 

 have described in T2 lysates a lytic agent which has a mode of action similar 

 to that of the proximal protein. This material, however, is relatively small in 

 size and has a molecular weight in the neighbourhood of 20,000. Although 

 the identity of this lytic material with that in the proximal tail remains to 

 be established, it is quite possible that there exist a number of lytic proteins, 

 either attached to or imbedded in the contractile portion of the proximal 

 protein. 



4. The removal of the distal portion of the tail of T2 can be demonstrated 

 using a variety of reagents and reactions (Kozloff et al., 1957), for example, 

 treatment with Zn++ or Cd++ cyanide complexes, hydrogen peroxide, papain, 

 freezing and thawing (Williams and Fraser, 1956). A study of this pheno- 

 menon by Kozloff and his associates (1957) has led to the conclusion that in 

 every case there occurs a splitting or hydrolysis of thiolester bonds, which 

 presumably attach the distal portion of the protein tail to the proximal part. 

 Electron micrographs taken during the course of treatment with a number of 

 these reagents suggest that the tail protein is uncoiled into five distinct 

 fibers prior to their complete removal from the proximal tail (Kellenberger 

 and Arber, 1955; Williams and Fraser, 1956; Kellenberger and Sechaud, 1957). 

 The fact that DNAase does not affect the fibers supports the view that they 

 are protein. Estimates of size of the fibers suggest that the whole of the 

 distal protein has a particle weight of around 1,000,000. After the distal 

 portion of the tail has been removed, Kozloff et al. (1957) fomid that 8 % of 

 the cysteine sulfur of the total phage protein was present in the supernatant. 

 The interpretation is made uncertain, since the supernatant fraction also 

 contains a variable number of viral tail "cores" (see next paragraph) whose 

 sulfur content is unknown. But the facts suggest that the distal protem may 

 be relatively rich in sulfur. This would sujjport the conclusion that the 

 splitting-off of the distal portion of the protein involves hydrolysis of a 

 thiolester bond. 



5. The presence of viral tail cores can be demonstrated in phage prepara- 

 tions after a variety of experimental procedures. By freezing and thawing 

 (Williams and Fraser, 1956), by treatment with hydrogen peroxide (Kellen- 

 berger and Arber, 1955) or the cyanide complexes of Cd++ or Zn++ (Kozloff 

 et al., 1957), one obtains preparations in which most virus particles show a 



