33. NUCLEIC ACIDS OF THE BACTERIAL VIRUSES 243 



one-sixtieth the DNA content of T2 (Tables I and IV). The DNA of this 

 phage does not have a complementary purine and pyrimidine composi- 

 tion, and a variety of lines of evidence have led to the conclusion that 

 it is a single-stranded form of DNA. 210 This observation poses most in- 

 teresting problems concerning its mode of replication. 



As yet little is known concerning the biochemistry of infection of phages 

 of this type. Kozinski and Syzbalski 211 using both P 32 and density label- 

 ing (by extensive substitution of thymine with 5-bromouracil, phages of 

 higher density are obtained) have demonstrated an extensive transfer 

 (50 %) of phosphorus from parental to progeny phage, with, however, ap- 

 parent dispersal of the material of the parental phage among the progeny. 

 No progeny phage . showing any of a variety of distinctive properties of 

 the parents could be found. 212 



The results seem to preclude the presence of intact parental DNA mole- 

 cules among the progeny. However, the original experiments concerning 

 the transfer of P 32 from parent to progeny are subject to criticism as 

 the multiplicity of phage particles (as contrasted to the multiplicity of 

 plaque-formers) was unknown and thus the apparent transfer of P 32 may 

 have been entirely from defective phages in mixed infection with viable 

 phages. 



The radiobiological properties of <£X174 differ considerably from those 

 of phages previously described. The sensitivity of this phage to decay of 

 incorporated P 32 at 4° is 10 times that of other phages; every P 32 decay 

 inactivates. 209 ' 213 



The capacity of host cells to support the growth of the related phage 

 S13 and the colony-forming ability of the cells are, under certain growth 

 conditions, quite close in their sensitivity to ultraviolet irradiation (E. S. 

 Tessman, personal communication, 1959), indicating that replication of 

 the phage requires the function of a major portion of the host genome. 

 Ultraviolet reactivation, an increase in the apparent survival of ultravio- 

 let irradiated phage if they are plated on lightly ultraviolet irradiated 

 host cells, is also observed with Si 3. 



210 R. L. Sinsheimer, J. Mol. Biol. 1, 43 (1959). 



211 A. W. Kozinski and W. Szybalski, Virology 9, 260 (1959). 



212 Nonradioactive phage were grown on heavily P 32 -labeled bacteria in heavily re- 

 labeled media. No progeny resistant to P 32 decay, as would be progeny incorporat- 

 ing the intact nonradioactive DNA of the parent, were found. Dense, 5-bromo- 

 uracil labeled phage were grown in cells in normal media lacking 5-bromouracil. 

 No progeny with the density of the parental phage were found. Normal phage were 

 grown in 5-bromouracil cells in media containing 5-bromouracil. No progeny with 

 the relatively low sensitivity to ultraviolet light of the parental phage (substitu- 

 tion with 5-bromouracil increases the ultraviolet sensitivity of this phage) were 

 found. 



213 I. Tessman, Virology 7, 263 (1959). 



