400 B. MAGASANIK 



TABLE VII 

 Nucleotide Composition of PNA from Miscellaneous Animal Sources 



" See page 395. 



Table VII presents the composition of PNA preparations isolated from 

 miscellaneous animal tissues. It is of interest that the PNA of cat brain*^ 

 and of carp muscle tropomyosin-^ have essentially the same composition 

 as liver PNA. The PNA of starfish^ and of sea urchin^^-^^ eggs similarly 

 possess the "high guanylic acid, high cytidylic acid" pattern found in all 

 other PNA preparations isolated from the tissues of animals. The composi- 

 tion of the sea urchin egg PNA did not change after fertilization during 

 the course of 48 hours of embryonic development.*^-" 



The problem of the heterogeneity of PNA in different cell fractions has 

 been studied in several laboratories.*^""*^ The cell nuclei were isolated in 

 citric acid or by centrifugation of a tissue mince at 700 X g. The elements 

 of the cytoplasm were fractionated by centrifugation (see Chapter 21). 

 PNA was not isolated, but the total polyribonucleotide composition of the 

 fractions determined directly. Some of the results obtained in these studies 

 are presented in Table VIII. There are no significant differences in nucleo- 

 tide composition between the different cytoplasmic fractions, which, 

 however, appear to differ from the nuclear fractions. The familiar "high 

 guanylic acid, high cytidylic acid" pattern of animal PNA was found in 

 every case. However, the nuclear PNA composition of different animals of 

 the same species seemed to vary appreciably. For instance, the composi- 

 tion of preparation 1 , which is the average of the nuclei obtained from the 

 livers of four rats, contains more guanylic acid than most of the other 

 preparations from nuclei. Even higher values for guanylic acid, which 

 would make the composition of nuclear PNA more closely similar to that 

 of cytoplasmic PNA, were found by Mclndoe in many batches of nuclei 

 (unpublished results quoted by Crosbie elal.)}^ The composition of nuclear 



"H. A. Deluca, R. J. Rossiter, and K. P. Strickland, Biochem. J. 55, 193 (1953). 



"D. Elson and E. Chargaff, Phosphorus Metabolism 2, 329 (1952). 



«8 A. Marshak, J. Biol. Chem. 189, 607 (1951). 



" W. M. Mclndoe and J. N. Davidson, Brit. J. Cancer 6, 200 (1952). 



