250 G. S. STENT 



possible to inquire whether during the latent period, and in particular during 

 the eclipse, there exist inside infected bacteria any incomplete particles which 

 are not yet infective but which already possess one or more of these three 

 attributes of the mature virus. Such investigations are greatly facilitated by 

 the use of radioactive tracers, which make possible the search for such 

 incomplete material through analysis of lysates for the presence of 

 noninfective but sedimentable, adsorbable, or antiserimi precipitable 

 radioactivity. 



Experiments have been carried out along these Hues in which bacteria 

 growing in media labeled either with radiophosphorus P^^ or radiosulfur S^^ 

 were infected and lysed prematurely at various times after infection (Maal^e 

 and Stent, 1952; Maalf)e and Symonds, 1953).i The results with P32 were 

 negative, in that durmg the eclipse no phosphorylated material can be found 

 which is sedimented, adsorbed, or antiserum-precipitated hke the parent 

 phage. After the end of the echpse, furthermore, the only phosphorylated 

 structures found to be endowed with these properties are the infective progeny 

 particles themselves. In other words, there do not appear to exist any 

 incomplete, DNA-containing phage particles which possess either the size and 

 shape, the attachment organs, or the antigenicity of the intact \Trus (Maaiy^e 

 and Stent, 1952). The results with S^^, however, were positive, in that several 

 minutes before the end of the eclipse, noninfective sulfurylated material 

 specifically precipitable by antiphage serum was found to be present (Maaloe 

 and Symonds, 1953). If the amount of precipitable phage antigen detected 

 at various times after infection is expressed in multiples of the total amount 

 of sulfur contained in a single mature bacteriophage, or phage equivalents, 

 then approximately 10-20 phage equivalents of phage antigen already exist 

 within the infected cell when the first mature progeny make their appearance. 

 The amount of incomplete, or surplus antigen, present after the termination 

 of the eclipse can be estimated by subtracting the number of infective phages 

 found by infectivity assays from the total number of phage equivalents of 

 antigenic sulfur recovered. The surplus antigen is then seen to attain a 

 maximum of 30-40 phage equivalents per infected cell 20 minutes after 

 infection and to remain at this level throughout the remainder of the latent 

 period. This noninfective, antigenic sulfur resides in particles which are 

 smaller, and hence less sedimentable, than the mature virus particles, but 

 nevertheless sufficiently large to be sedimented by high-speed centrifugation 



^ As has already been discussed in detail in previous chapters, bacteriophages are com- 

 posed of roughly equal proportions of deoxyribonucleic acid (DNA) and protein, of 

 which the former harbors practically all of the phosphorus of the particle (in the poly- 

 nucleotide phosphate diester bonds) and the latter all of the sulfur (in the amino acids 

 methionine and cysteine). Hence, phages groA\TQ in a medium containing either P^- or 

 S'* are labeled only in their DNA or only in their protein, respectively. 



