232 A. GAREN AND L. M. KOZLOFF 



1. Attachment 



The phage attaches by its tail to the host cell. The initial attachment 

 reaction occurs between a specific cell waU receptor and the tail fibers of the 

 phage, and may be reversible. Almost immediately after the initial reaction 

 a more permanent bond of unknown nature is formed. 



Cell Surface 



^ 



T 2 



Attachment 



^I.^^^^^^^^'^^^^^^^Z^' 



Alteration of Tip 

 of Phage Tail 



S^^^^^^^^ 



"^Z^^/^J^z/yTyZ^i 



Fig. 12. Diagrammatic representation of the reactions involved in T2 invasion. 



2. Alteration of the Tip of the Phage Tail 



There is strong evidence that the fibers at the tip of the tail are unwound 

 and eventually removed after permanent attachment to the cell wall. Zinc, 

 tightly bound to cell waU protein, is essential for the unwinding and removal 

 of the tail fibers. The tail fibers appear to be attached to each other (and to 

 the tail core) by thiolester bonds. It is probably during this stage of invasion 

 that the tail enzyme, which hydrolyzes cell waU material, is exposed. 



3. Contraction of the Phage Tail 



The evidence for contraction is based on the morphological changes which 

 occur under various conditions and on the striking parallehsm of the invasion 



