STRUCTURAL AND CHEMICAL ARCHITECTURE OF HOST CELLS 45 



Vendrely et al. (1956) have studied the ratio of arginine to DNA-P in 

 the nuclei and nucleoproteins of many animals. They have recorded that 

 with a very few exceptions, e.g., carp, the transformation of somatic nuclei 

 to sperm nucleus is accompanied by a marked increase in the ratio of 

 molecules of arginine to atoms of DNA-P, i.e., from 0.33-0.41 to 

 1.10-1.27. 



Estimations have been made of the histone and DNA content of nuclei 

 during different stages of division (Bloch and Godman, 1955). The synthesis 

 of these substances proceeded simultaneously, resulting in their doubling 

 prior to ceU division. 



e. Lipids. Stoneburg (1939) and Bounce (1943) demonstrated the presence 

 of these important structural elements in their preparations of nuclei. A 

 number of workers have studied the fractionation of these lipids (Bounce, 

 1955). Of particular interest are the findings of the absence of cerebrosides 

 and of significant amounts of neutral fat and phospholipid, consisting mainly 

 of lecithin and cephalin. Stoneburg had earlier reported relatively large 

 amoimts of ether-insoluble hpids which were then presumed to be sphingo- 

 myelin and cerebrosides, Levine and Chargaff (1952), who also found nuclear 

 lipids insoluble in petroleum ether, suggested that much of the nuclear hpid 

 may exist as polymeric entities. The latter workers found ethanolamine, a 

 constituent of one type of cephalin, in amounts in nuclear lipid equal to that 

 of choline, the base present in lecithin and sphingomyelin. Only small 

 amounts of serine, thought to be derived from serine cephalin, were found. 



A study of phosphohpid synthesis in regenerating rat liver (Johnston 

 et al., 1954) has shown a high rate of synthesis of phosphohpid (cephalin, 

 lecithin, and sphingomyelin) coincident with mitosis. This was not affected 

 by colchicine, which stops development at metaphase. It was suggested, 

 therefore, that Hpid synthesis was associated with either interphase or 

 prophase, but not with anaphase or telophase. 



/. The DNA Content of Nuclei. The following circumstances have led us 

 to beheve that BNA plays a particularly important role in the determination 

 of heredity: 



1. BNA is a component of all chromosomes in all types of cells. 



2. Highly purified BNA is active in bacterial transformation in pneumo- 

 cocci. Hemophilus, etc. 



3. BNA is the major component (about 97 % of the total) transferred 

 from a phage to the bacterium it infects, and therefore determines not only 

 the synthesis of viral BNA but also of viral protein. 



In this context we are led to the propositions that (1) the BNA content 

 of the nucleus is characteristic of its content of genetically active substance; 

 (2) in multicellular organisms, diploid somatic cells should have identical 

 BNA contents; (3) diploid somatic cells will contain twice the BNA present 



