226 A. GAEEN AND L. M. KOZLOFF 



the usual denaturing agents wliich break hydrogen bonds, such as heat and 

 alkaH. The phage DNA can escape when the phage is exposed to arginine, 

 heat, or alkah, even though the head protein remains attached to the tail 

 structure. There is very little evidence on the nature of the bonds attaching 

 the head structure to the tail. The head protein can be almost completely 

 separated from the tail by prolonged alkali treatment, but this property does 

 not clearly implicate any particular bond. 



3. Role of Zinc 



The highly specific action of complexes of the zinc group metals on the 

 tail protems of T2 bacteriophage (Kozloff and Henderson, 1955), as listed in 

 Table III, appeared to duplicate the action of the cell waU on the phage 

 particle. In 1957, Kozloff and his co-workers (Brown and Kozloff, 1957; 

 Kozloff and Lute, 1957a) furnished direct evidence that zinc, tightly bound 

 to the ceU waU, was necessary for the alteration of the phage tail during 

 invasion. 



It was shown that there was an enzyme in T2 which could partially degrade 

 the host ceU waU (Barrington and Kozloff, 1954, 1956). However, intact T2 

 was enzymaticaUy inactive and the enzymatic activity was exposed only 

 after the tail fibers were removed (Brown and Kozloff, 1957). Zinc tightly 

 bound to the ceU wall was necessary for the exjDosure of this enzyme during 

 phage-ceU waU interaction (Kozloff and Lute, 1957a). Zinc is known to be an 

 essential component of a number of dehydrogenases (VaUee et al., 1956). 

 Although there is no evidence yet on the location of such enzymes in E. coli, 

 a study of enzyme localization in the related B. megatherium (Storck and 

 Wachsman, 1957) has shown that a considerable variety of dehydrogenases 

 are indeed located in the cell membrane. It may also be pertinent that, for 

 one particular zinc enzyme, triose phosphate dehydrogenase (Racker, 1954), 

 it has been found that thiolester bonds are formed and cleaved during the 

 action of this enzyme. In any case, it appears that the phage particle utilizes 

 some normal cellular component which contains zinc. 



4. Contraction of Proximal Tail Protein 



After T2 has interacted with cell walls, the tail fibers are completely re- 

 moved and the particles appear to have a short, thick tail with the core 

 protruding (Fig. 8— KeUenberger and Arber, 1955). Probably the main 

 reason for the hesitation in beheving that the proximal tail protein did actu- 

 ally shorten and thicken (i.e., contract) was that little evidence was available 

 on how much of the tail structure of the intact particle was composed of the 

 fibers. Lacking this information, it seemed not unlikely that the tail fibers 

 might reach halfway up the tail (KeUenberger and Arber, 1955) and that the 

 thickening might be an artifact of the electron micrograph. However, it is 



