INTRACELLULAR MULTIPLICATION OF BACTERIAL VIRUSES 263 



bacteria infected with phages aheady UV-inactivated prior to infection or in 

 infected bacteria whose survival as infective centers has been destroyed by 

 UV-irradiation at early stages of the eclipse period. If the infected bacteria 

 are UV-irradiated at later stages of the eclipse period, however, when some 

 antigenic precursor protein is already present in the cells, then phage antigen 

 continues to be synthesized at a rapid rate even though further DNA synthesis 

 and, a fortiori, production of infective progeny has been abohshed by the irra- 

 diation. Thus it seems that while at the outset of the intracellular phage growth 

 DNA and protein syntheses are connected with one another in some neecessary 

 way, so that stopping one will stop both, the two processes become indepen- 

 dent of each other once the mechanism for formation of phage-specific protein 

 has been established within the infected cell. 



V. Fate of the Infecting Phage Particle 



A. Functional Differentiation and Injection 



The work discussed in the preceding sections has given some insight into 

 the manufacture of the substance of the progeny virus particles within the 

 phage-infected cell. In this discussion it became clear that the two principal 

 components of the progeny phages, i.e., protein and DNA, are synthesized 

 separately and that their union is the all but last act of the intracellular 

 reproduction process. From the investigations to be recounted now, which are 

 concerned with what actually happens to the parental phage particle when 

 it infects the host cell and presides over the reactions leading to its manifold 

 reduphcation, it has been learned that the separation of protein and DNA of 

 the infecting virus is, in fact, also the first act of the intracellular reproduction 

 process. These experiments can be thought to have taken their inception 

 with the observation that T-even bacteriophage particles are inactivated by 

 osmotic shock (Anderson, 1949, 1953). Osmotic shock engenders the release 

 of the DNA from the proteinaceous membrane of the phage head, leaving 

 behind DNA-free "ghosts" still capable of adsorbing to and even killing 

 bacterial host cells (Herriott, 1951). The osmostic release from the phage 

 head makes the DNA accessible to such degradative enzymes as deoxy- 

 ribonuclease (DNAase), from whose action the head membranes had previously 

 protected it. Contemporaneously with the finding of osmotic disruption, the 

 phenomenon of "superinfection breakdown" — to be discussed in more 

 detail below — had been discovered; it indicated that, as in osmotic shock, so 

 also in the process of infection the DNA of the parental phage particle becomes 

 exposed to the action of degradative enzymes (Lesley et al., 1950, 1951). 

 Hershey and Chase (1952) then demonstrated in the wake of these observa- 

 tions the existence of independent fimctions of the two viral moieties, protein 



