30. PHOTOCHEMISTRY OF NUCLEIC ACIDS 



83 



100 

 Dose (ergs/mm. 2 ) 



150 x<o 3 



Fig. 14. Ultraviolet inactivation of transforming DNA from hemolytic strepto- 

 cocci group H, strain Challis: (a) for intraspecific transformation (of streptomycin 

 resistance) and (b) for interspecific transformation, receptor strain sbe type I/II 

 [from R. Pakula, E. Hulanicka, and W. Walczak, Bull. acad. polon. set., Classe II, 7, 

 217 (1959)]. 



hit" type of process 171 but this is apparently not a general phenomenon 

 (see Fig. 13). Complex inactivation curves have been reported for two 

 genetic markers of pneumococcal TDNA, but it is claimed that a "one- 

 hit," or first-order, process is involved. 172 



Figure 14 exhibits the course of ultraviolet inactivation of TDNA from 

 hemolytic streptococci group H for homologous and heterologous trans- 

 formation of streptomycin resistance. 173 The differences in sensitivity are 

 very marked; but were much less so for pneumococcal TDNA, where the 

 heterologous receptor was the sbe type I/II strain of hemolytic streptococci 

 group Ff. 173 



Similar types of inactivation curves exhibiting two exponentials have 

 been reported by others 172 ' 174 for pneumococcal TDNA; and Beiser and 

 Ellison 174 have actually fractionated pneumococcal TDNA on ECTEOLA 

 columns into components with sensitivities corresponding to the two seg- 

 ments of the inactivation curve for the unfractionated DNA. 



It has been suggested that the inactivation rate of TDNA is markedly 

 dependent on the concentration, but since the results are based only on the 

 measurement of residual activities — and some of the solutions were op- 



171 S. Zamenhof, G. Leidy, E. Hahn, and H. E. Alexander, J. Bacteriol. 72, 1 (1956). 



172 L. J. Tolmach and L. S. Lerman, Radiation Research 7, 128 (1957). 



173 R. Pakula, E. Hulanicka, and W. Walczak, Bull. acad. polon. set., Classe II 7, 

 217 (1959). 



174 S. M. Beiser and S. A. Ellison, 7th Intern. Congr. Microbiol., Stockholm, 1958 

 Paper No. 4f (1958). 



