THE NUCLEIC ACID CONTENT OF TISSUES AND CELLS 43 



penicillin to a culture of these bacteria decreased the absolute rate of PNA 

 synthesis more than that of DNA. These authors suggest that "the rate of 

 cell protein synthesis appears to be controlled by the percentage weight of 

 nucleic acids in the cells, while the nucleic acid synthesis appears to be more 

 directly determined by the nutritive properties of the medium than protein 

 synthesis." 



From his studies on continuous cultures of Polytomella caeca, Jeener-^^ 

 has developed the very important concept that "the rate of increase of cell- 

 ular proteins is proportional to the quantity of RNA which is in excess of 

 a basal quantity concerned with the renewal of the existing protein." Only 

 in this way could he account for the unexpected decrease in the amount of 

 PNA per unit protein which occurred in cultures when cell multiplication 

 and, therefore, protein synthesis, was slowed down by limitation of either 

 phosphate or organic nutrients, such as ethanol and acetate. 



Gale and Folkes-'*"' ^ also report a strong positive correlation between 

 the rate of protein synthesis and the nucleic acid content of the cells, in 

 this case. Staphylococcus aureus. Although chloramphenicol, aureomycin, 

 and terramycin completely inhibited protein synthesis in this organism, 

 they stimulated the rate of formation of nucleic acid. 



Dirx^i^ found that the PNA content of the spores in a variety of molds 

 ranges from 0.145 pg. per spore for Penicillium to 1.93 pg. for Aspergillus. 

 In yeast cells, Ogur et a/.^^ report that the DNA-P per cell increases in 

 direct ratio to the degree of ploidy; so do dry weight, PNA, and metaphos- 

 phate, but with a much wider experimental variation. 



Little can be said about the nucleic acid composition of viruses. Reviews 

 are available by Knight.^i* Beard,^!^ and Davidson.^ Both PNA and DNA 

 are found in viruses, but, as Knight pointed out, only PNA has been ob- 

 served so far in plant viruses, whereas either PNA or DNA or both are 

 present in animal viruses. In plant viruses (e.g., tobacco mosaic, tomato 

 bushy stunt, and southern bean mosaic) the PNA concentration ranges 

 from 6 to 40 % on a dry weight basis, whereas for a few animal viruses it is 

 always below 10 %. The DNA concentration varies between 2 % in influ- 

 enza virus^is to 40 % in T2 bacteriophage,22o each of which contain some PNA. 



XII. Conclusions 



Certain definite associations between the nucleic acids and tissue metab- 

 olism can be seen in the results described in this review. Whereas changes 



21* R. Jeener, Arch. Biochem. and Biophys. 43, 381 (1953). 



"6 (a) E. F. Gale and J. P. Folkes, Biochem. J. 53, 483 (1953); (b) ibid. p. 493. 



217 J. Dirx, Biochim. et Biophys. Acta 8, 196 (1952). 



218 C. A. Knight, Cold Spring Harbor Symposia Quant. Biol. 12, 115 (1947). 



219 J. W. Beard, Physiol. Revs. 28, 349 (1948). 



220 A. Taylor, J. Biol. Chem. 165, 271 (1946). 



