94 



D. SHUGAR 



TABLE IV 

 Quantum Yields for Virus Inactivation 



a F. M. Uber, Nature 147. 148 (1941). 



6 G. Oster and A. D. McLaren, J. Gen. Physiol. 33. 215 (1950). 



c A. Kleczkowski, Biochem. J. 56, 345 (1954). 



d D. E. Lea, "Actions of Radiations on Living Cells." Cambridge Univ. Press, London and New York, 

 1955. 



e From A. Siegel and A. Norman [Virology 6. 725 (1958)] assuming* for Ul strain is about 4 X 10" 5 . 



f D. J. Fluke, quoted by E. C. Pollard, "The Physics of Viruses." Academic Press, New York, 1953. 



" M. R. Zelle and A. Hollaender, J. Bacteriol. 68, 210 (1954); values are approximate means of values ob- 

 tained at various wavelengths in range indicated. 



McLaren's 98 value for TMV is based on a 50% scattering correction; this 

 is certainly too large and the quantum yield is therefore too high, perhaps 

 by as much as 30%. The apparent independence of # with wavelength for 

 Tl and T2 phages in Table IV is in serious disagreement with the marked 

 wavelength dependence reported by Fluke 197 for Tl irradiated either in the 

 wet or dry state. Zelle and Hollaender 200 present a valuable discussion of 

 the possible influence of experimental conditions on these discrepancies. 

 Luria's 194 emphasis on the importance of quantum yield measurements for 

 action spectra determinations is no less valid today. But experimental 

 difficulties are still formidable and relative sensitivities at different wave- 

 lengths continue to be used. 



The action spectra of the common (Ul) strain of TMV (Fig. 18) and, 

 to a lesser extent, Rous sarcoma virus, differ appreciably from those for 

 other viruses, and cannot be readily accounted for. Siegel and Norman 169 

 therefore compared the relative sensitivities of TMV strains Ul and U2 

 at three different wavelengths with those of the infectious RNA com- 

 ponents from these strains, the latter of which exhibit identical sensitivities. 

 U2 is about 5 times as sensitive as Ul at 280 mit and 253.7 m/z, but both 

 strains exhibit equal sensitivity at 226 m/x ; at 254 mju the RNA components 

 extracted from each virus, following partial inactivation, were found to 

 have been reduced in infectivity to the same extent as the parent virus. 

 It was therefore concluded that at 254 mn inactivation is due solely to 

 RNA absorption and this is considered to be substantiated by the fact 



