t2 and other bacterial viruses 463 



B. The Heterogeneity of Viral Protein 



Study of the process of replication in the bacterial viruses has led to an 

 increasing amount of information indicating different physiological functions 

 for various portions of the viral protein coat. It is not certain whether these 

 can be correlated with discrete molecular entities, that is, whether the 

 protein coat consists of a number of individual proteins held together by 

 hydrogen bonding and van der Waals' forces, or whether the protein 

 sheet is a continuous structure held together by the usual covalent bonds 

 and exhibiting specific physiological properties in localized areas. Perhaps 

 both alternatives exist; certainly in the case of the distal fragment of the 

 tail protein of T2, the covalent linkage of the thiolester bond is the mode of 

 attachment to the proximal portion of the particle. 



At the present time, there is visual evidence for the existence of at least 

 five components of the protein sheath, although none of these, as yet, has 

 been isolated and chemically characterized completely. Further, it should 

 be emphasized that evidence in tliis respect has been obtained primarily 

 from the study of T2, with the major findings confirmed with T4. However, 

 as yet, none of the other coliphages has been studied; one might expect 

 important differences with the odd-numbered T phages. At the moment, we 

 have evidence for the following distinguishable protein fractions: 



1. The protein sheath of the head. 



2. A protein of the proximal portion of the tail, having possible contractile 

 functions in viral invasion (and differing from 3). 



3. A protein of the proximal portion of the tail, possessing lytic activity 

 for bacterial cell walls. 



4. The protein of the distal portion of the tail, serving as the agent for the 

 initial attachment of the virus to the bacterial host. 



5. The protein of the so-called "core structure" of the tail of the viral 

 particle. 



Evidence for the existence of each of these components is as follows: 

 1. Lanni and Lanni (1953) were able to show by serological techniques the 

 existence of at least two viral proteins, one associated with the head and 

 another with the tail of the T2 particle. By separating the noninfectious 

 donuts and rodiike structures present in prematurely lysed infected cells or in 

 infected cells treated with proflavin, they were able to show that an antigen 

 giving rise to neutralizing antibodies was localized in the rodlike structures, 

 that is, presumably the viral tail, while another antigen, recognized by com- 

 plement fixation tests, was localized in the phage heads (donuts). 



There is also evidence of the differential susceptibility of the head protein 

 to various reagents. For example, treatment of T2 with 0.1-0.2 M arginine 

 leads to alteration of the virus head, but leaves the proximal tail intact 



VOL. I — 31 



