224 A. GAREN AND L. M. KOZLOFF 



appear to contain DNA, indicating that injection does not occur with the 

 type of cell wall preparation used in these experiments. 



2. Removal of Tail Fibers 



The tail of T2 is composed of several protein components (see Section II), 

 and each probably plays a specific role during invasion. The total amount of 

 protein in T2 corresponds to a molecular weight of 125,000,000. It has been 

 calculated that, of the total phage protein, the tail structure represents 12 %, 

 with about 3 % in the tail core and 1 % in the tail fibers (Kozloff e^ al, 1957). 

 Since there are 4 or 5 fibers, each fiber has a molecular weight of perhaps 

 250,000. It is of interest that, by radiation studies, Pollard and Setlow (1956) 

 calculated that the attachment of T2 to its host cells is mediated by a portion 

 of the T2 structure having a molecular weight of 186,000. 



The only well-established covalent bonds for linking separate polypeptide 

 chains, such as the components of the phage tail, are the disulfide and phos- 

 phodiester bonds. The evidence on the nature of the bonds in the phage tail 

 implicates a siilfur-containing bond (Kozloif e« al., 1957). It appears not to be 

 a disulfide bond. The evidence also argues against a phosphate ester bond, a 

 peptidic bond, or an oxygen ester or ether bond. On the basis of the mor- 

 phological changes of the phage particle caused by various chemical and 

 physical treatments, it seems likely that thiolester bonds are the main bonds 

 between the tail fibers and the rest of the tail. Every treatment known to 

 disrupt thiolester bonds causes the tail fibers to become partially unwound, 

 or completely unwound, or removed from the phage tail. 



It should be emphasized that this type of evidence for a thiolester bond as 

 the main structural link in the phage tail is quite circumstantial. However, it 

 is difiicult to obtain direct evidence. From an estimation of the amount of 

 cysteine sulfur in the tail fibers, it was calculated that there are at most 300 

 thiolester bonds in the trail structure (Kozloff et al., 1957). These would be 

 difficult to detect because the turbidity of phage preparations greatly limits 

 the use of colorimetric methods. 



Table III lists the efi'ect of various chemical and physical treatments on 

 the structure of T2; some of the typical morphological alterations are illus- 

 trated in Fig. 9. The details of the treatments are given in the references. 

 Papain, which has thiolesterase activity, is the only enzyme so far reported 

 to affect the structure of T2 phage. The fact that several reagents which 

 have little or no effect on disulfide bonds can alter the tail structure would 

 seem to eliminate the possibility that disulfide bonds are the main structural 

 cross links. These reagents are pH 10 buffer, iV-ethyl-maleimide, and NHoOH. 

 The removal of the tail fibers in pH 10 buffer would also eliminate hydrogen 

 bonding between SH and amino groups as the main hnkage, since this bond 

 is not broken in alkaline solution (Benesch et al, 1954). In general, the degree 



