THE INITIATION OF BACTERIOPHAGE INFECTION 227 



now clear, from the work of Kellenberger and Sechaud (1955) on free tail 

 cores, that these fibers comprise only the structure at the end of the tail, as 

 illustrated diagrammatically in Fig. 6. 



Evidence that the tail fibers comprise only the tip of the tail of the intact 

 phage is provided by the electron micrographs of T2 treated by pH 10 

 glycine buffer (Kozloff, 1958). It can be seen in Fig. 10 that in the early 

 stages of the action of the alkaline solution on the virus particle the tail 

 fibers are unwomid from the tip of the tail. The head loses its distinctive shape 

 and, apparently, also its nucleic acid. After more prolonged treatment the 

 head and the tail fibers are completely removed from most of the particles. 

 However, even after the removal of the fibers, the tails are approximately 

 their normal length and width. From most of the free tails there appears 

 another structure, which probably is the tail core. 

 ' These results on the aUvahne degradation of the virus particle clearly show, 

 not only that the fibers comprise only the tail tip, but that umder these con- 

 ditions the proximal tail does not contract. Contraction does occur when the 

 pH of the alkaline solution containing these free tails is subsequently 

 lowered to 6.6 (Fig. 10c), This behavior is analogous to that of myosin, which 

 contracts only when the pH is below 10, presumably because the Mg-myosin 

 complex and adenosine triphosphate have the same charge at pH 10 (Morales, 

 1956). 



The analogous behavior of the proximal tail protein and myosin led to an 

 examination of other properties of the proximal tail that might be similar to 

 those of myosin (Kozloff, 1958). Under certain conditions, EDTA (ethylene- 

 diaminetetraacetic acid) inhibits the contraction of actomyosin (Friess, 1954; 

 Tonomura et al., 1957). Furthermore, it has been shown that EDTA can 

 cause a relaxation of contracted muscle fibers (AVatanabe and Sleator, 1957). 

 It has been found that sodium EDTA does not affect attachment of T2 to the 

 intact host cell, but that it does prevent the formation of infective centers 

 (Kozl'off and Henderson, 1955) by preventing injection of DNA into the host 

 cell (Kozloff, 1958). A similar effect was shown for the staphylococcal bacter- 

 iophages (Rountree, 1955). In this connection it is worth mentioning the 

 experiments of Luria and Steiner (1954), which showed that there is a calcium 

 requirement for the penetration of T5 DNA into the host cell. T5 has a long 

 thin tail and it is possible that a high concentration of calcium is necessary 

 for the contraction of the tail protein in order to allow the subsequent 

 release of the DNA. 



A strikingly analogous pattern of the properties of invasion mechanism of 

 the phage tail and of actomyosin can be seen in Table IV. Various mono- 

 valent cations affect the inhibition of myosin ATPase (adenosine triphos- 

 phatase) by EDTA. In the presence of Na+ and Li+, EDTA completely 

 inhibits myosin ATPase. Substitution of K"*" or NH4+ for Na"*" completely 



