190 ROBERT L. SINSHEIMER 



of the cell wall takes place after which the DNA of the phage, mostly con- 

 tained in its "head" is "injected" into the bacterium. 29 The internal protein 

 and dibasic amines also enter, but most of the protein of the phage remains 

 external to the bacterial cell and appears to play no further role in the 

 infective process. 30 



At this stage no infective particle can be found attached to or within 

 the bacterial cell and the phage is said to be in a "vegetative" phase. 34 

 The period from infection to the first intracellular appearance of infective 

 particles is known as the "eclipse period." 35 



Consequent to the entry into the cell of the viral DNA, which appears 

 to be composed of several molecules, synthesis of host DNA and ribonu- 

 cleic acid (RNA) largely ceases. An obligate synthesis of certain proteins 

 essential to the phage replication takes place. These are not the phage anti- 

 gens; some are certainly enzymes required to make specific viral compo- 

 nents. Synthesis of a specific RNA is also observed. 



At about 6 minutes after initiation of infection the synthesis of new viral 

 DNA can be detected. The rate of synthesis increases until a limiting rate 

 of about 10 phage units per cell per minute is reached at about 10 minutes. 

 Synthesis of phage antigen commences at about 8 minutes. 



At 10 to 12 minutes the first mature intact progeny phage particles can 

 be found inside the infected cell. At the time these appear, a pool of about 

 40-50 units of phage DNA and 10-20 units of phage antigen has been pro- 

 duced. The pool of phage DNA includes a large fraction, if not all, of the 

 parental DNA. The rates of DNA and protein synthesis and of phage mat- 

 uration appear to be such as to maintain the pools at approximately con- 

 stant level. DNA and protein appear to be drawn from the pools into 

 mature phage at random, and an individual particle may contain DNA 

 molecules made at different times. Formation of a mature phage particle 

 appears to be an irreversible process. 



Accumulation of mature phage particles in the cell continues until ter- 

 minated by a process which ordinarily disrupts the cell about 21 minutes 



29 A. D. Hershey and M. Chase, J. Gen Physiol. 36, 39 (1952). 



30 However, the process of attachment of the phage to the bacterium has profound 

 effects on the metabolism of the latter, even in the absence of phage DNA. Thus 

 phage "ghosts" obtained by osmotic shock of T2 phage and containing about 3% 

 of the phosphorus and almost all of the protein of T2 phage 31 upon adsorption to 

 bacterial cells bring about a cessation of RNA synthesis and ultimate lysis of the 

 cell. 32 ' 33 The mechanism of this action and its relation to the events of normal 

 bacteriophage infection is unknown. 



31 R. M. Herriott and J. L. Barlow, J. Gen. Physiol. 40, 809 (1957). 



32 R. M. Herriott and J. L. Barlow, J. Gen. Physiol. 41, 307 (1957). 



33 I. R. Lehman and R. M. Herriott, J. Gen. Physiol. 41, 1067 (1958). 



34 A. H. Doermann, Cold Spring Harbor Symposia Quant. Biol. 18, 3 (1953). 



35 A. H. Doermann, J. Gen. Physiol. 35, 645 (1952). 



