30. PHOTOCHEMISTRY OF NUCLEIC ACIDS 



91 



200 220 240 260 280 

 A(nyi) 



Fig. 18. Action spectrum for B. megaterium bacteriophage M-5 [from R. M. 

 Franklin, M. Friedman, and R. B. Setlow, Arch. Biochem. Biophys. 44, 159 (1953)] 

 and of the common strain of TMV [from A. Hollaender and J. W. Oliphant, J. Bac- 

 teriol. 48, 447 (1944)]. 



absorption spectrum; 165 but this is not as satisfactory as observations 

 based on biological activity such as infectivity of RNA from TMV or 

 transforming DXA. 



Nevertheless, it must be admitted that the evidence from action spectra 

 is strongly in favor of nucleic acids as the primary receptors of radiation in 

 many biological phenomena. The extent to which proteins are involved 

 cannot, however, be considered as equally well established. This is due 

 largely to the experimental difficulty of obtaining a sufficient number of 

 points on the action spectrum. In at least one instance where this has been 

 achieved, 186 for a Bacillus megaterium bacteriophage, the use of additional 

 wavelengths in the neighborhood of 280 mp. resulted in an action spectrum 

 suggestive of the involvement of the protein component (Fig. 18). By 

 contrast, the action spectrum for the common strain of TMV, 187 shown in 

 the same figure, is inexplicable in terms of either the protein or nucleic 

 acid moieties. We shall return to this question below in connection with 

 viruses. 



186 R. M. Franklin, M. Friedman, and R. B. Setlow, Arch. Biochem. Biophys. 44, 

 159 (1953). 



187 A. Hollaender and J. W. Oliphant, J. Bacteriol. 48, 447 (1944). 



