THE BIOCHEMISTRY OF PLANT VIRUSES 85 



confirmed. Fraenkel-Conrat observed that coprecipitation with virus protein 

 increased the apparent infectivity several hundredfold. It would appear 

 that this step of "reconstitution "would be a useful procedure when studying 

 the biological activity of virus nucleic acids. 



K. The Action of Various Agents upon the Infectivity of the Virus 



As has been mentioned, the present evidence is that the infectivity of 

 the tobacco mosaic virus resides in its nucleic acid component. If this is so, 

 then chemical or physical agents which inactivate the virus must act in 

 one of two ways. Either they must modify the nucleic acid component so 

 as to make it inactive, or they must interfere with the virus protein in such 

 a way as to prevent the emergence of the nucleic acid, which must presumably 

 precede the multiplication of the virus. Quite recently it has been shown that 

 the nucleic acid from the tobacco mosaic virus, if inoculated into plants, 

 causes the production of infectious virus after a time lag of 19 hours, while 

 whole virus inoculated similarly takes at least 10 hours longer to start 

 multiplying (Schramm and Engler, 1958). Thus any treatment which might 

 interfere with the removal of the protein coat of the virus will cause inactiv- 

 ation in some degree. This could explain, for example, the effects of sub- 

 stituting various chemical groupings on the surface of the virus (MiUer and 

 Stanley, 1942) or of the indirect action of ionizing radiation on dilute solutions 

 of virus (Lea et al., 1944). The direct action of radiation of this type is 

 probably due to direct hits on the nucleic acid core of the virus (BuzzeU 

 etal., 1956) and a dramatic demonstration of this has been given by Lauffer 

 and his colleagues, who showed that the action of X-rays on the whole 

 virus could not be detected by viscosity measurements, but that the nucleic 

 acid prepared from irradiated virus was appreciably disaggregated (Lauffer 

 et al, 1956). 



Perhaps the most important single agent used in inactivation studies is 

 formaldehyde. Formaldehyde, of course, is not a substance of much use for 

 the inactivation of tobacco mosaic virus, but as it is a substance used for the 

 inactivation of other viruses the chemistry of the action is of general interest. 

 (We once had occasion to examine plant material originally imported into 

 the United States of America in the form of sap, containing about 5 % v. /v. 

 of 40 % formaldehyde solution to render it "sterile." After being stored 

 for some 2 years under these conditions viable virus was isolated without 

 difficulty.) 



The action of formaldehyde on proteins, and in particular nucleoproteins, 

 is exceedingly complex. The various reactions which it causes have been 

 reviewed at length by French and Edsall (1945). As far as the infectivity 

 of tobacco mosaic virus is concerned the inactivation follows first-order 



