BIOLOGICAL ROLE OF DEOXYPENTOSE NUCLEIC ACIDS 469 



A number of characters were transferred, including nutritional, fermenta- 

 tive, drug-resistance, and antigenic traits. Only one new property was ob- 

 served to be transferred at a time to an individual cell, however, a feature 

 by which transduction appears more closely related to transformation than 

 to sexual recombination in microorganisms. The sedimentability of the 

 agent and its stability to deoxyribonuclease, and the relatively low fre- 

 quencies of transduction, at present distinguish the process from trans- 

 formation. The active agent has now been traced to the phage particles 

 liberated upon lysis of the donor strain. ^^^ The lysis may either be the spon- 

 taneous lysis by a symbiotically carried phage or that occasioned by intro- 

 duction of the same temperate phage into a donor strain upon which it has 

 a lytic action. The occasional effective phage particle appears to have 

 conveyed a genie factor from the donor strain (its previous host) and intro- 

 duced it (not necessarily establishing phage infection at the same time) 

 into the new strain. Analogous transfers of two characters in S. typhosa by 

 a virulent phage have been reported. ^'"^ 



III. Other Aspects of DNA Function 



Although one would be unjustified from present knowledge either to 

 assert or to deny that nuclear gene material of all species is composed of 

 DNA, one should certainly not be misled into assuming that all DNA has 

 a specific genetic role. We have seen that there is little reason to hold, for 

 example, that all of a pneumococcus-transforming DNA preparation is 

 made up of specific genetic determinants, whether identified or unidentified. 

 It may very likely be as unjustified as assuming all proteins to be enzymes. 

 It has often been suggested that some of the chromatin DNA of chromo- 

 somes has a function different from that of the rest (heterochromatin and 

 euchromatin^^*). So, too, there have been indications that a certain part of 

 the DNA of bacteriophages could undergo ultraviolet irradiation^^*--'^ or 

 suffer atomic disintegration^'^ without effect upon phage proliferation. 

 These considerations lead us again to recall the fact that parental phage 

 DNA-phosphorus and DNA-adenine are recovered only incompletely (35 

 to perhaps 50%) in the phage progeny. The conserved portion is not 

 passed on intact, but is distributed, at least somewhat diluted, among the 

 progeny, and it is not uniquely conserved, but again diluted, and partially 



2'3 N. D. Zinder, Cold Spring Harbor Symposia Quant. Biol. 18, 261 (1953). 



"'* L. S. Baron, S. B. Formal, and W. Spilman, Proc. Soc. Exptl. Biol. Med. 83, 292 



(1953). 

 *'^ J. Schultz, Cold Spring Harbor Symposia Quant. Biol. 12, 179 (1947). 

 "'« S. Benzer, J. Bacteriol. 63, 59 (1952). 

 "" R. Dulbecco, J. Bacteriol. 63, 199 (1952). 

 "8 A. D. Hershey, M. D. Kamen, J. W. Kennedy, and H. Gest, /. Gen. Physiol. 34, 



305 (1951). 



