394 S. GARD AND O. MAAL0E 



temperatures about 85°C. He found, in addition, that virus in which the 

 nucleic acid had thus been exposed had acquired sensitivity to ribonuclease. 



Fraenkel-Conrat and Williams (1955) ^Jrepared pure nucleic acid and pure 

 protein from TMV and claimed that, although each fraction was by itself 

 inactive, a partial "reconstitution" of the virus with restoration of infect- 

 ivity was obtained if the j^rotein was allowed to polymerize in the presence 

 of nucleic acid. Similar observations were reported by Hart (1956a) and by 

 Commoner et al. (1956). Since it has now been convmcingly shown that the 

 pure nucleic acid alone may produce infection, the true significance of the 

 reconstitution phenomenon is at present somewhat doubtful. 



Gierer and Schramm (1956), after treatment of the virus with 50 % phenol 

 in the cold, were able to isolate a protein-free nucleic acid fraction with a 

 residual activity corresponding to about 2 % of the original, i.e., of the same 

 order as that reported for the reconstituted virus. The free nucleic acid was 

 rapidly inactivated by ribonuclease, which has no effect upon the intact 

 virus. On the other hand, its infectivity was not affected by anti-TMV hyper- 

 immune serum, which completely neutralized the virus. Fraenkel-Conrat (1956, 

 1957) independently found that the nucleic acid fractions obtained by treat- 

 ment with alkaline buffer, SDS, or 67 % glacial acetic acid are infectious as well. 



Phenol treatment, according to Gierer and Schramm, has also been applied 

 to encephalomyocarditis (EMC), West Nile, and poho virus (Colter et al., 

 1957a,b) and to eastern equine encephaUtis (EEE) virus (Wecker and 

 Schafer, 1957), in all cases with successful isolation of an infective nucleic 

 acid fraction. However, in these cases the starting material consisted of 

 unpurified virus, hence the resulting preparations were composed largely of 

 tissue cell nucleic acid. Myxoviruses similarly treated have so far failed to 

 yield any active fraction (Schafer, personal communication). A liberation of 

 the nucleic acid containing group antigen of the latter viruses by means of 

 the much milder ether treatment (Hoyle, 1952) likewise results in complete 

 inactivation ( Andre wes and Horstmaim, 1949). 



From these observations it is obvious that the TMV, and perhaps the 

 EMC and EEE virus nucleic acids contain the entire genetic information 

 necessary for the synthesis of the respective viruses, as was previously shown 

 for bacteriophage. It seems not unreasonable to generalize this conclusion and 

 assume that the nucleic acid in all viruses represents the genome, that it 

 alone carries the reproductive capacity, and determines the type and rate of 

 synthesis induced in the host cell as well as the ultimate fate of the infected 

 ceU. 



The naked nucleic acid seems to be very labile, however, easily inactivated 

 by heat and by treatment with nuclease. One of the functions of the non- 

 nucleic acid components of the virus seems to be that of stabilizing and pro- 

 tecting the nucleic acid. In addition such components may serve the purpose 



