ISOLATION AND COMPOSITION OF PENTOSE NUCLEIC ACIDS 379 



warm. If the solution is left in the refrigerator for a few hours, the virus crystallizes 

 out in the form of small birefringent needles; they may be left at 1°C. for a few days, 

 when the mass of crystals will be found to adhere to the bottom of the container and 

 the mother liquor may be decanted without difficulty. The crystals are then dissolved 

 in 0.1 M disodium phosphate or a neutral buffer, as they form cloudy suspensions in 

 plain water. Spinning at 5000 r.p.m. removes the pigmented material which by now is 

 insoluble. 



4. Isolation of Nucleoprotein from Microbial Tissues 



The protoplasm of microorganisms is especially rich in nucleoprotein. 

 Bacteria contain as much as 15% (dry weight) nucleic acid, of which 

 60-75 % is of the pentose type. In spite of the high concentration of PNA 

 in bacterial cells, it is difficult to obtain bacterial PNA-protein prepara- 

 tions free from DNA-protein and comparable in purity to the PNA-pro- 

 teins isolated from animal cells. The obstacles encountered are the difficulty 

 of breaking up bacterial cells without harm to their labile constituents, the 

 presence of potent nucleases in bacterial extracts, and finally, the presence 

 of DNA-protein throughout the cytoplasm rather than in a discrete remov- 

 able structure such as the nucleus. 



Recently, Parsons has described the isolation of a PNA-protein free 

 from deoxyribose from Clostridium perfringcnsr^ The nucleic acid was 

 extracted from lyophilized cells with 0.14 M NaCl and purified by precipi- 

 tation with methanol at —10° C. and with ammonium sulfate. 



The situation is more favorable in yeasts primarily because of their low 

 DNA-protein content. Thus the isolation of PNA-proteins from acetone- 

 dried ground yeast has been accomplished by Khouvine.^^ Several nucleo- 

 proteins which differed in nucleotide composition were obtained by iso- 

 electric precipitation at different pH's. The significance of this observation 

 will be discussed in the section on nucleotide composition. 



III. The Nature of Pentose Nucleoprotein 



The isolation of material consisting of nucleic acid and protein is in itself 

 no proof that an entity such as "nucleoprotein" really exists. The material 

 isolated may be a conglomerate consisting of a random collection of dis- 

 tinct protein and PNA units held together by the attraction of oppositely 

 charged groups located on their surfaces. Such salt-like combinations of 

 protein and PNA could be present in the cell, or the two components could 

 meet and become attached to one another in the course of the isolation 

 procedure. In either case, the proper approach would be to separate the 

 protein and nucleic acid moieties and to study their individual properties. 



" C. H. Parsons, Jr., Arch. Biochem. and Biophys. 47, 76 (1953). 

 2' Y. Khouvine and H. De Robichon-Szulmajster, Bull. soc. chim. biol. 33, 1508 

 (1951). 



