33. NUCLEIC ACIDS OF THE BACTERIAL VIRUSES 233 



presented as yet, while the results of Volkin et a/. 131 indicate an absence of net RNA 

 synthesis during T7 infection. 



Watson and Maal0e 87 demonstrated that 30-40% of the phosphorus of 

 parental T3 phage was transmitted to progeny phage. Mackal and Kozloff 180 

 similarly found a transfer of 20-30% of parental DNA phosphorus to 

 progeny DXA phosphorus and a somewhat lesser (0.6-0.8 X) transfer of 

 parental DXA nitrogen to progeny DXA nitrogen. However, they ob- 

 served that at any multiplicity of infection about 6-12% of the parental 

 phosphorus appeared as nonsedimentable phosphorus in the medium, and 

 that in mixed infection with live T7 and ultraviolet killed X 15 -labeled 

 T7, as much nitrogen was transferred to progeny as with live labeled T7. 

 Because of these results, Mackal and Kozloff concluded that the transfer 

 to progeny was largely a nonspecific transfer involving reincorporation into 

 progeny DNA of degradation products of parental DXA. 



3. Radiobiological Distinctions between the Tl, T3, andT7 

 Group and the T5 Plus T-Even Group 



Several lines of evidence 6 have led to the hypothesis that the Tl, T3, 

 T7 group is radiobiologically distinct from the T2, T4, T6, T5 group, 

 and it has been suggested that this distinction may be the result of a 

 partial genetic homology between the former group and the host genome. 

 The possibility of such a homology is favored by the similarity of nucleo- 

 tide composition of the DXA of this phage group and the DNA of the 

 host cell. 



Differences between these two groups exist with respect to such prop- 

 erties as ultraviolet sensitivity per milligram of DNA 6 (somewhat lower 

 with the Tl, T3, T7 group), multiplicity reactivation of ultraviolet dam- 

 aged phage (very limited with the Tl, T3, T7 group; very frequent with 

 the T2, T4, T6, and To group), 47 ' 181 and the character of the changes of 

 the ultraviolet sensitivity of the phage-bacterium complex during the early 

 stages of infection 688 ' 89 (with the T2, T4, T6, and To group the sur- 

 vival curves of the complex remain exponential, but with rapidly dimin- 

 ishing slope as infection proceeds; with the Tl, T3, T7 group the sur- 

 vival curves quickly become multi-hit, with increasing multiplicity as the 

 infection proceeds, but with a constant ultimate slope at high dose). 



The two groups may also be distinguished with respect to the effect 

 of ultraviolet irradiation on the capacity of the host cell to support their 

 multiplication. 182 - 183 The capacity of E. coli B to support the growth of 



180 R. P. Mackal and L. M. Kozloff, /. Biol. Chem. 209, 83 (1954). 



181 I. Tessman and T. Ozaki, Virology 4, 315 (1957). 



182 T. F. Anderson, /. Bacleriol. 56, 403 (1948). 



183 E. S. Tessman, Virology 2, 679 (1956). 



