88 S. S. COHEN 



aconitase. Other systems of the fraction are briefly summarized by Hoge- 

 boom and Schneider (1955). Considering the state in which it is obtained, it 

 is difficult at this time to correlate the biological relations of this fraction 

 with its chemical properties. At present, the cell sap constitutes a splendid 

 fishing pool for the elementary stages in the traming of an enzymologist. 



G. Polymer Synthesis in Cytoplasm and Nucleus 



1. Methodology 



Before examining data on the synthesis of proteins and nucleic acid at the 

 enzymatic level within specific cell fractions, it is desirable to consider the 

 variety of approaches used to locaHze these functions within more or less 

 intact cells and to summarize the relatively large body of information arising 

 from such studies. These studies are of particular interest for the design of 

 experiments by virologists. The approaches used include the following: 



1. Incorporation of a labeled precursor into the test system. Cell fractiona- 

 tion and autoradiography have been employed to estimate the extent of 

 incorporation into various cell parts. Numerous modifications of this type of 

 experiment have been made in order to obtain data on the possible kinetic 

 interrelations of cell fractions and components. 



2. Separation of intact cells into enucleate and nucleate fragments. The 

 metabolic capabilities of such organized fragments have then been explored 

 by a variety of techniques, including the isotopic approach indicated above. 

 In recent years these experiments have been performed for the most part on 

 two selected types of differentiated giant cells, the alga, Acetabularia, and the 

 protozoan, Amoeba. It may be noted that the induction of giantism in virus- 

 susceptible mammalian cells in X-irradiated tissue cultures (Cieciura et al., 

 1957) may now permit the performance of many of these kinds of experiments 

 with this infectable material. 



3. Specific enzymatic ehmination of cell components without cell destruc- 

 tion. The use of enzymes, such as ribonuclease to degrade basophihc com- 

 ponents in a variety of hving cells and lysozyme to eUminate the cell wall 

 and produce viable bacterial protoplasts, permits a comparison of the meta- 

 bohc capabilities of normal and partially degraded cells. 



4. Nutritional deficiencies and genetic lesions have been exploited in 

 bacteria to produce specific deficiencies of cell parts. 



5. Inhibitors have been similarly employed to induce specific deficiencies. 

 These have included chemical substances, such as chloramphenicol and 

 penicilHn, or physical agents, such as ultraviolet irradiation. 



2. Protein Synthesis 



a. Relations to Problems of Protein Structure. We wish to know if protein 

 synthesis can occur throughout all parts of a cell, i.e., at all the sites of 



