IV NUCLEIC ACIDS AND NUCLEOPROTEINS 9O5 



Many other investigators have employed microspectrophotometric methods in 

 order to determine the nucleic acid contents of malignant cells. Mellors etal. (1952) 

 reported the following values for the total nucleic acids of the nuclei of interphase 



cells : 



Normal epithelial cells = 910"^^ g/nucleus 

 Squamous carcinoma cells = 35- lo"^^ g/nucleus 



The latter group could be divided into three subgroups with average values of 

 17, 38 and 67- 1 o"^2 g/nucleus. In a subsequent study Mellors et al. (1954) found 

 that 13 types of mouse tumors had an average content of nucleic acid per nucleus or 

 a chromosome number that was approximately twice that of normal diploid 

 somatic nuclei. Lymphoma, lymphatic leukemia and a sarcoma had normal con- 

 tents of nuclear nuclei acid. Petrakis and Folstad (1954) also found that the DNA 

 content of a lymphoma (designated number two) was close to the normal diploid 

 value (2N). Lymphoma number one had an average of DNA per cell of 4N to 

 8N. Since this latter lymphoma presumably contains a tetraploid number of 

 chromosomes, this would indicate a premitotic build-up of DNA in the presence 

 of aneuploid chromosome numbers. Attention may also be directed to the investi- 

 gations of Ludford (1954) on modifications of nuclear structure in tumors; the 

 histochemical studies on the ribonucleic acids in basocellular and spinocellular 

 carcinoma (Prunieras, 1954): the findings of Villa et al. (1955) concerning the 

 nucleic acids of normal and leukemic blood cells; and Ackerman etal. (1951) who 

 have reported that Hodgkin's cells contain more ribonucleoprotein than the 

 reticulum cells of origin. 



The nuclei of fowl tumor cells contain considerably more RNA than the nuclei 

 of cells from several normal tissues (Mclndoe and Davidson, 1952) which has 

 been generally observed by other investigators. Several compositional and meta- 

 bolic studies have been carried out on the nuclei isolated from normal or cancerous 

 cells (Mclndoe and Davidson, 1952; Magasanik, 1955). The nuclear RNA has 

 a different purine and pyrimidine composition than the RNA of the cytoplasmic 

 fractions. As mentioned above, tumor cell nuclei may contain more RNA than 

 most normal cell nuclei ; however, there is no evidence to suggest that the nuclear 

 RNA of the malignant tissues differs in qualitative aspects from the RNA of 

 normal cell nuclei. Attention is called to the critical comparison made by Kay 

 et al. (1956) of cell nuclei isolated by aqueous and non-aqueous procedures. 



Cerecedo et al. (1955) found that the DNA and RNA decreased in concentration 

 as the tumor (Sarcoma 256) increased in size. Azo dye induced hepatomas have 

 a much higher DNA potassium ratio than the liver of the control rats (Rodriques 

 et al., 1955) The DNA content of nuclei was determined in normal and tumorous 

 tissue of brain by Heller and Elliott (1954). The nuclear density, as determined by 

 these investigators, was higher in the brain tumor than in the normal brain tissues. 

 Levy et al. (1953) determined the RNA and the DNA per tumor cell following 

 the inoculation of an ascites thymoma in mice. Both RNA per cell and DNA 

 increased up to 6-8 days following the inoculation of the tumor and then declined. 



Irradiation of C57BI mice resulted in a large increase in the RNA per thymic 

 cell (Weymouth et al., 1955). If these animals were thigh shielded during irradia- 



Literature p. Qig 



