30. PHOTOCHEMISTRY OF NUCLEIC ACIDS 93 



The subject of energy transfer in photobiological and radiobiological systems has 

 been dealt with in several recent publications and symposia. 193 



IX. Viruses 



Viruses are undoubtedly the most useful and fascinating systems for 

 photochemical studies, as well as those which have most profited from 

 such investigations since they are, in effect, nucleoproteins exhibiting a 

 variety of biological activities and may be irradiated either in vitro or in 

 the intracellular state where they behave as components of more complex 

 integrated biological systems. The limited scope of this chapter permits 

 only a brief discussion of the photochemistry of viruses in relationship to 

 the nucleic acid components. Broader aspects of virus photochemistry have 

 been dealt with by Luria, 194 Pollard, 195 and Kleczkowski. 196 



Ultraviolet inactivation of virus infectivity usually follows a first-order reaction, 

 but numerous exceptions are known; 39 - 194 some of them are quite puzzling, e.g., in- 

 activation of Tl phage is first-order in the dry state, but not in solution. 197 For a 

 polio virus the complex inactivation curve has been interpreted as due to the pres- 

 ence of two strains of varying sensitivity. 198 The effect of irradiation conditions on the 

 shape of the survival curves of Tl phage has been extensively investigated by Hill 

 and Rossi 199 ; although no definite conclusions could be drawn, the results are none- 

 theless of considerable value for future investigations. In a number of instances a 

 small percentage of the residual activity has been found remarkably resistant to ir- 

 radiation 194 ' 200 ; for Tl and T2 phages this has been ascribed 200 to multiplicity reacti- 

 vation, 194 but it is unlikely that such is the case for infectious RNA from TMV of 

 which about 1% of the residual activity is remarkably radiation resistant. It should 

 also be recalled that transforming DNA exhibits a similar behavior. 



Quantum yields have been obtained for only a few viruses and are shown 

 in Table IV. 201 " 203 In general, these values are based on corrections for 

 scattered light which may be subject to considerable error, e.g., Oster and 



193 (a) "Basic Mechanisms in Radiobiology" (J. L. Magee, M. I). Kamen, and R. L. 

 Platzman, eds.), Natl. Research Council Publ. No. 305, Washington, D. C, 1953; 

 (b) I. A. Vladimirov and S. Konev, Biofizika 2, 3 (1957); (c) Symposium Soc. de 

 chim. phys., in J. chim. phys. 55, (11-12) (1958); (d) Symposium Faraday Soc, 

 Nottingham, 1959 (Discussions Faraday Soc. in press). 



194 S. E. Luria, in "Radiation Biology" (A. Hollaender, ed.), Vol. II, Chapter 9. 

 McGraw-Hill, New York, 1955. 



195 E. C. Pollard, "The Physics of Viruses." Academic Press, Now York, 1953. 



196 A. Kleczkowski, Advances in Virus Research 4, 191 (1957). 



197 D. J. Fluke, Radiation Research 4, 193 (1956). 



198 J. Fogh, Proc. Soc. Exptl. Biol. Med. 89, 464 (1955). 



199 R. F. Hill and H. H. Rossi, Radiation Research 1, 282, 358 (1954). 



200 M. R. Zelle and A. Hollaender, ./. Bacteriol. 68, 210 (1954). 



201 F. M. Uher, Nature 147, 148 (1941). 



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



203 D. E. Lea, "Actions of Radiations on Living Cells." Cambridge Univ. Press, 

 London and New York, 1955. 



