IV 



NUCLEIC ACIDS AND NUC LEO P ROTEI NS 



907 



DNA- 

 i 



(GS) 



•►cRNA"- 



(GDS) 



— ^ Complex- 



Substrates 



II. 



R-tide? 



/ 



Inducer"; 



• Protein ♦-♦.Complex 



Products 



Con|ugated 

 -surface 

 protems 



Common pool of 



acid soluble 

 nbo-nucleotides 



Substrates 



PURINE PRECURSO RS 

 Bases 



Nucleosides 

 Glycine / 

 formate 



COMMON PRECURSORS 



Con|ugated 

 -surface 

 protem<. 



Adenosine and 

 guanosine mono- 

 di- and tri- 

 phosphates 

 and coenzymes 



Bases 



Nucleosides- 

 Aspartate — 

 Orotate 



Carbamyl aspartate 



Undine and 

 cytidine mono-, 

 di-, and tri- 

 phosphates 

 and coenzymes 



Fig. 5. Tentative relationships between 

 genes, enzyme-forming systems, enzyms 

 and cell surfaces. RNA = ribonucleic 

 acid; DNA = deoxynucleic acid; 

 AA == amino acids; EFS = enzyme 

 forming system; GS = gene system; 

 GDS = gene-dependent EFS; GIS = 

 gene-independent EFS. 



(?) Purines and pyrimidines. Ehrlich ascites tumor can synthesize RNA pyrimidine 

 from the same precursors as are utilized by liver (Lagerkvist et al., 1954). In these 

 studies it was observed that uracil '^N was incorporated into the RNA pyrimidines 

 at approximately the same rate as orotic acid-'-N. The utilization of uracil-2-''*C 

 in rat liver and in acetylaminofluorine induced hepatomas was investigated by 

 Rut man et al. (1954a) and Cantarow et al. (1955). Exogenous uracil was utilized by 

 the hepatomas, but not in the normal rat liver. Uracil served as a precursor of 

 uridylic acid but not of the purine nucleotides or of the deoxypentose pyrimidine 

 nucleotides. This enhanced utilization of uracil in the hepatomas may reflect the 

 rapid growth that is occurring in these tissues. Proliferative activity in normal tis- 

 sues may also be accompanied by a measurable incorporation of uracil. Eidinoff 

 et al. (1956) injected ureidosuccinic acid-^'*C, a pyrimidine precursor, into rats 

 bearing human tumor transplants. Seven hours after administration of this com- 

 pound the specific activity of thymine was highest in the tumor, followed bv in- 



Literature j>. gig 



