164 BACTERIOPHAGES 



for T4 by Jesaitis and Goebel (1953, 1955) and for T5 by Weidel, 

 Koch, and Bobosch (1954). These results seem to show that the 

 opening of a hole in the phage particle and release of DNA does 

 not call for the action of a bacterial enzyme. 



DNA can also be released from phage T2 following interaction 

 with ion exchange resins (Puck and Sagik, 1953) or with cad- 

 mium cyanide (Kozloff and Henderson, 1955), and from T5 by 

 interaction with citrate or merely by removal of calcium (Lark 

 and Adams, 1953). In the last two cases, the reaction is ac- 

 companied by loss of adsorbability of the phage ghosts and al- 

 terations at the tip of the tail of the phage particle. The relation 

 of these facts to normal injection is obscure, however, especially 

 since the injection by T5 requires calcium and is presumably in- 

 hibited by citrate (Luria and Steiner, 1954). If a phage enzyme 

 is involved in the release of DNA, it remains to be demonstrated. 



The morphological aspects of penetration by T2 were clarified 

 by Kellenberger and Arber (1955) and Williams and Fraser 

 (1956) (Chapter IV). Fibers at the tail-tip of the phage particle 

 attach to the bacterial surface, exposing the central pin which 

 actually penetrates the cell wall. This penetration could be 

 purely mechanical (Williams and Fraser, 1956) or might be aided 

 by enzymic processes. 



Phage T2 inactivated by formaldehyde still adsorbs to the host 

 cell, and kills it with low efficiency. However, the DNA of the 

 inactivated particles is not injected into the bacteria but remains 

 within the phage membrane in a form resistant to deoxyribonu- 

 clease. It could be supposed that formaldehyde inactivates an 

 enzyme in the phage particle but in view of the complicated 

 nature of the penetration process, the action of formaldehyde can 

 be explained in other ways. 



c. Puncture of the Bacterium 



Infection of bacteria by T2 initiates a complex series of cellular 

 reactions many of which have to be considered in any discussion 

 of mechanisms of penetration, especially because no satisfactory 

 conclusions can be reached at this time. 



