BIOLOGICAL ROLE OF DEOXYPENTOSE NUCLEIC ACIDS 467 



accumulate in a precursor pool from which phage is steadily produced 

 after a few minutes of the latent period have elapsed. '^'^ Some of the more 

 general findings are indicated in Fig. 2. 



One of the important questions concerning precursors for phage DNA 

 appears to be how the parental nucleic acid is utilized. There is good evi- 

 dence from several sources that half or somewhat more of the parental phage 

 p32 165,157,169 g^j^^j puriue carbon"" is discarded in low-molecular debris'" at 

 each cycle of infection.'*^ '^^ There does not appear to be, therefore, a 

 uniquely retained stable portion, and there is no indication whether the 

 "discarded" fragments come from a genetically unessential portion or from 

 determinants themselves, which may be degraded as a result of their func- 

 tioning. In bacteria'^^ and, as already mentioned, in animal tissues, the 

 enhanced metabolic exchange of DNA at the time of cell division does not 

 usually appear to bring about the loss of the phosphorus or other markers 

 already incorporated. 



e. Symbiotic Phages and Other Viruses 



Most phages have not yet been sufficiently well prepared and analyzed 

 to indicate whether or not they infect their hosts with DNA as do the T 

 phages. It is, however, known that some of them contain DNA. This is true 

 of certain staphylococcal phages, and the control of the DNA synthesis 

 in infected staphylococci appears to be decisive for phage multiplication. '*** 



One group of phages which have recently been much studied are the 

 symbiotic or "temperate" phages which may be carried for many genera- 

 tions in an infected bacterial host, and only from time to time spontane- 

 ously lyse an occasional host cell to liberate free virus. Such phages are 

 relatively difficult to prepare in pure form, and little is as yet known about 

 their chemical nature, although DNA has been found associated with some 

 of them. 



When these temperate viruses do lyse their host, there are some signs of 

 involvement of DNA. It is possible to induce lysis by some of these carried 

 phages when the host culture is irradiated with ultraviolet or treated with 

 certain mutagenic agents.'^® This observation itself has occasioned the in- 

 ference that the "provirus" precursor was associated with the DNA and 

 the genetic equipment of the host cell. Of interest in this connection is the 

 fact that the symbiotic virus, X, of E. coli K-12 is transmitted in sexual 

 recombination processes in some form of linkage with the entities responsible 

 for the genetic marker, galactose IV. '^'^ 



1" O. Maal0e and J. D. Watson, Proc. Natl. Acad. Set. U. S. 37, 507 (1951). 



194 L. W. Labaw, V. M. Mosley, and R. W. G. Wyckoff, J. Bacteriol. 59, 251 (1950). 



195 W. H. Price, J. Gen. Physiol. 33, 17 (1949). 

 '9« A. Lwoff, Ann. inst. Pasteur 84, 225 (1953). 



1" E. Lederberg and J. Lederberg, Genetics 38, 51 (1953). 



