STRUCTURAL AND CHEMICAL ARCHITECTURE OF HOST CELLS 197 



duplication. More recently, the theoretical problem of the specificity of inter- 

 action between identical molecules in general has been explored as a possible 

 function of the charge interaction between electric dipole oscillators (London 

 forces) (Jehle, 1950, 1957; Yos et al, 1957). 



It has been suggested that these forces lead to a template action resulting 

 in the direct assembly of identical molecules and can help to explain gene 

 stability, specificity, and assembly; in a word they may truly produce "self- 

 duplication." However, it should be noted that, as a consequence of the work 

 of Yos et al. (1957), they consider it umiecessary and undesirable to invoke 

 the splitting af the DNA duplex into separate daughter chains; this result 

 has already been obtained in the work of Meselson and Stahl (1958). 



In earlier sections we have considered the question of the stability of DNA 

 and its apparent lack of turnover. Notable exceptions are the cases described 

 by Zamenhof ef al. (1956a, b) and by Coughlin and Adelberg (1956) as a conse- 

 quence of thymine deficiency. In an attempt to explain the obvious function 

 of DNA and its apparent stability in some dynamic mechanism, a hypothesis 

 was presented in Fig. 25 of a partial cleavage of phosphodiester bonds in 

 portions of a polynucleotide chain, with the simultaneous formation of amino 

 acid anhydrides. Such derivatives might subsequently condense with other 

 amino acids, releasing phosphate for recondensation with the previously 

 freed 3' hydroxyl in the polynucleotide chain. 



That DNA does help directly to organize amino acids mto proteins is sug- 

 gested by: (1) the concomitant synthesis of histone during DNA synthesis in 

 normal interphase, and (2) the abolition of nuclear incorporation of amino 

 acids into protein as a result of theactionof deoxyribonuclease. A remarkable 

 related observation of Brunish and Luck (1952) has not yet been explained. 

 Nucleohistone of hver was capable, albeit rather slowly, of incorporating 

 carboxyl-labeled amino acids m a form which did not give rise to radioactive 

 carbon dioxide through the use of ninhydrin, implying the formation of 

 peptide bonds. 



It is important to note that little or no evidence is available to support any 

 of the possible mechanisms described above concerning the mode of action of 

 DNA. However, these mechanisms, particularly modifications of that involv- 

 ing the formation of intermediate amino acid nucleotide complexes, are now 

 being discussed widely to attempt to explain the way in which UNA 

 directs protein synthesis. 



2. RNA as a Template 



That UNA can control the synthesis of KNA directly in all cases is not 

 entirely certain. Although cytoplasmic UNA can be synthesized in enucleate 

 Acetabularia, the data on enucleate Amoeba suggest the contrary conclusion. 



