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E, A. EVANS, JK. 



type; recent work (Volkin and Astrachan, 1956) would seem to exclude 

 rigorously the presence of RNA previously reported. The T7 and, probably, 

 T3 phages appear to be exceptions to the above; only 71 % of the P is present 

 as DNA (Lunan and Sinsheimer, 1956). Most virus preparations contain 

 measurable quantities of lipid material (about 2 %), but it is uncertain 

 whether this is a contaminant or an integral part of the viral structure. 



II. General Structure of Coliphage Particles 



Figure 1 represents a summary of current information with respect to the 

 functional anatomy of coliphage T2. Many of these structural features 



HEAD PROTEIN 



-DNA 



lOOOA 



DISTAL 

 >F?OTEIN 



Fig. 1. Diagrammatic representation of coliphage T2. 



probably occur in other members of the T series (most of them have been 

 confirmed for T4) but the other T phages have not yet been studied in tliis 

 respect. It is generally believed tliat the nucleic acid of the virus particle is 

 concentrated within the head and is sheathed by a protective coat of protein. 

 This view is based on the facts: (1) that the intact virus particle is resistant 

 to the action of DNAase; (2) that on rapid dilution of concentrated saline 

 solutions of T2 the viral nucleic acid is liberated into the medium and the 

 remaining protein "ghosts" are seen (under the electron microscope) to 

 retain the spermlike shaj)e of the intact particle, although the head is 



