260 G. S. STENT 



(1957) that the number of incomplete phage protein doughnuts per cell is no 

 greater in proflavine than in normal lysates seems puzzling from this point of 

 view, since one would have expected an intracellular accumulation of these 

 incomplete structures if only their incorporation into mature phage but not 

 their synthesis had been arrested by the drug. 



IV. Synthesis of Nonprecursor Materials 



A. Ribonucleic Acid 



Thus far in our discussion of phage multiplication we have been concerned 

 with the synthesis inside the infected bacterium of bacteriophage "pre- 

 cursors," i.e., of structures which upon their maturation will constitute the 

 matter of the progeny phages. We shall now turn our attention to some 

 "nonprecursor" materials connected with the reproductive processes, i.e., 

 substances which, though synthesized by the phage-infected bacterium, are 

 not ultimately incorporated into infective virus particles. 



Ribonucleic acid (RNA) is the principal phosphorylated constituent of 

 E. coli and hence the destination of most of the phosphorus assimilated by the 

 cells during their normal growth. The rapid RNA synthesis of the bacteria 

 comes to a sudden halt upon their infection by T-even phages and very little 

 increase in total RNA content of the infected culture can be discerned during 

 the remainder of the latent period (Cohen, 1947; 1948a; Manson, 1953). Tracer 

 experiments in which P^^ is added to the bacterial culture only after infection 

 suggested, however, that an appreciable amount of the label does enter an 

 RNA fraction during phage growth, i.e., that some RNA synthesis might be 

 occurring in the infected cells after all and that the previoi^sly observed post- 

 infection constancy in RNA content represents a balance of breakdown and 

 resynthesis (Hershey, 1953a). More complete studies, m which was examined 

 the incorporation of P^^, not only into RNA, but also into the four individual 

 ribonucleotides — cytidylic, adenylic, uridylic, and guanylic acids — definitely 

 established the existence of an RNA synthesis during intracellular phage 

 growth (Volkin and Astrachan, 1956a, 1957). These studies showed, not only 

 that radioactive ribonucleotides can be isolated from the digest of the RNA 

 of the infected cells, but also that the radioactive label does not enter each 

 of the four ribonucleotides at the same relative rate at which the ribonucleo- 

 tides of uninfected E. coli bacteria would have acquired P^- under analogous 

 labeling conditions, i.e., that the postinfection synthesis concerns a species of 

 RNA of base composition different from that of the over-all host cell RNA. The 

 amount of postinfection RNA present at any time is rather small compared to 

 the total RNA content of the bacterium but, if expressed in multiples of the 

 weight of nucleic acid per T-even phage particle, nevertheless attains a level 



