230 A. GAKEN AND L. M. KOZLOFF 



proximal tail protein. Since sodium EDTA does not affect tlie action of intact 

 phage on cell walls (Barrington and Kozloff, 1956; Kozloff and Lute, 1957a), 

 although it inhibits the contraction of the proximal tail proteins, it seems 

 Ukely that the enzyme is immediately exposed after the removal of the tail 

 fibers or after only a slight contraction, and is probably located close to the 

 distal end of the uncontracted proximal tail. Although the viral enzyme has 

 not been isolated and has been only partially characterized, the occurrence 

 of typical phage enzyme activity in a nonsedimentable form in lysates 

 (Brown, 1956; Koch and Jordan, 1957) suggests that the enzyme is synthe- 

 sized quite independently of the proximal tail protein. Koch and Jordan 

 (1957) have claimed that the phage enzyme is relatively small, having a 

 molecular weight of about 20,000. This would also differentiate it from the 

 relatively large particulate proximal tail protein. 



It is difficult to ascribe to any one particular reaction between the phage 

 and the cell the phenomena of irreversible attachment and cell death (see 

 Sections II and V). Once the virus has been altered the attachment is irre- 

 versible, but irreversible attachment occurs even with zinc-deficient cell walls 

 (Kozloff and Lute, 1957a) where there can be little or no removal of phage 

 tail fibers. Presumably, an irreversible bond between the phage and the cell 

 wall is formed before the tail fibers are split off. In fact, the firm binding of 

 the tail fibers might play an important role in holding the phage particle on 

 the cell wall after the fibers have been unwound from the tail core. This 

 would serve to keep the enzyme in close contact with its substrate. 



C. Release of Phage DNA 



The factors controlling the release of phage DNA from its protein covering 

 and the passage of the DNA into the cell are poorly understood. Some of the 

 physical forces which might affect the passage of DNA into the cell have been 

 discussed recently in a theoretical paper by Ore and Pollard (1956). It was 

 shown that ordinary forces, such as linear Brownian movement, and the 

 centrifugal puU exerted by oscillatory thermal movements, could largely 

 account for the rate of DNA injection. However, no consideration was given 

 to the changes which occur in the viral tail structure or to the effect of electro- 

 static interaction between the phage DNA and protein. Both of these factors 

 would be expected to influence greatly the rate of DNA release. 



Part of the difficulty in studying the injection mechanism has been due 

 to the difficulty in isolating experimentally this phase of the process from 

 other reactions. Kecently, T2, altered by treatment with cadmium cyanide 

 complexes in a manner presumably identical to that produced by interaction 

 with the cell wall, has been used to study the factors affecting the release of 

 DNA (Kozloff and Lute, 1957b). After alteration the tail is 50 % shorter and 

 it can be estimated that the central hole in the tail (after the removal of the 



