INTRACELLULAE MULTIPLICATION OF BACTERIAL VIRUSES 273 



reproduction of other phage strains, such as Tl, T7, A, PI, and P2, leaves the 

 nucleus largely intact throughout most of the latent period (Luria and Human, 

 1950; Murray et al, 1950; Murray and Whitfield, 1953; Kellenberger, 1953; 

 Wliitfield and Murray, 1954), It is conceivable that the previously mentioned 

 increase in intrabacterial DNAase activity and its possible epiphenomenon, 

 superinfection breakdown, are related to the dissolution of the host nucleus 

 in T-even, uifected cells, since there is neither any increase in DNAase activity 

 (Pardee and WiUiams, 1953; Wormser and Pardee, 1957) nor any establish- 

 ment of superinfection breakdown (French et al., 1951) in bacteria infected 

 with Tl, T3, T7, or A, i.e., with phages which permit the nucleus to remain 

 intact. Most likely, it is the destruction of the host cell nucleus by the T-even 

 phages which is responsible for their suppression of ceUular growth and 

 enzyme induction, since the integrity of the nucleus appears to be essential 

 for bacterial enzyme synthesis (McFall et al., 1958). Some other striking 

 differences in behavior between the T-even phages and various phage strains 

 have led to the following notion^ (Stent, 1958): The T-even phages are charac- 

 terized by high UV sensitivity and high multiplicity reactivability of the 

 free virus particles, low radiosensitivity of the "capacity" of the bacterial 

 host, and frequent genetic exchange between vegetative phages in multiple 

 infection. They can, therefore, dispense with the integrity of the host cell 

 nucleus, which they destroy anyway at the outset of their growth. A second 

 group of phages, which includes Tl, T3, T7, A, and P22, are characterized by 

 low UV sensitivity and low multiplicity reactivability of the free virus 

 particles, high radiosensitivity of the capacity of the bacterial host and even 

 higher radiosensitivity of the capacity for the reproduction of irradiated 

 phages, existence of UV reactivation, and its attendant appearance of new 

 genotypes and infrequent genetic exchanges between vegetative phages in 

 multiple infection. This second group, therefore, requires the integrity of the 

 host ceU nucleus, with which these phages undergo repeated genetic inter- 

 actions in the course of their vegetative growth. This same idea might also 

 account for the exclusion of Tl, T7, or A from bacteria simultaneously infected 

 by a T-even particle (Delbriick and Luria, 1942; Luria and Delbriick, 1942; 

 Delbriick, 1945b; Weigle and Delbriick, 1951), since phages Hke Tl, T7, 

 or A should not prosper in a cell in which the presence of a T-even phage 

 has already destroyed the bacterial nucleus necessary for their repro- 

 duction. 



One important type of intracellular bacterial virus multiplication has been 

 almost entirely neglected in this chapter, namely, that ensuing not from 

 infection by an exogenous virus particle, but from induction of a prophage 

 within a lysogenic ceU. This process is discussed in Chapter 9 of this volume, 



^ The phenomena referred to here are actually outside the province of the chapter 

 and are elucidated in Chapters 8 and 10, Vol. II. 



VOL. II — 18 



