94 S. S. COHEN 



amoebae incorporate twice the amoirnt of metliionine used by the nucleate 

 half. Mazia and Prescott suggest that the amino acid is activated by the 

 rate-limiting amount of cytoplasm, which then transfers the active precursor 

 to the nucleus. 



It should be noted that protein synthesis in the cytoplasm in Amoeba is 

 quite significant, and, in agreement with the work on Acetabularia, the studies 

 on Amoeba have shown that the cytoplasm is capable of independent protein 

 synthesis. Such a conclusion is in agreement with the conclusions derived 

 from work on reticulocytes (basophilic nonnucleated erythrocytes), which 

 also appear capable of synthesis of globin and hemin (London et al., 1950; 

 Borsook et al., 1952). 



Functional enucleation may be accomphshed, at least in part, in a variety 

 of biological materials, of which the reticulocyte is one. In many adult 

 tissues, mitosis may be a rare event among many metabolizing cells actively 

 synthesizing protein. In such systems, e.g., nerve, liver, etc., general protein 

 synthesis is at least separable from the duplication of DNA and histones. 

 Similar results may be obtained with thymine-requirmg bacteria deprived of 

 thymine (Earner and Cohen, 1954) or with ultraviolet-irradiated bacteria 

 (Kelner, 1953; Kanazir and Errera, 1954), in both of which protein and RNA 

 are synthesized in the absence of DNA synthesis. 



In many respects a cell is functionally enucleate during division (Brachet, 

 1957). In amoebae, growth and protein synthesis stop at this time (Prescott, 

 1955) and P^^ uptake also decreases 50 % in this organism (Mazia and 

 Prescott, 1954). In early development of the frog (mitil gastrulation), RNA 

 synthesis stops during the rapid series of mitoses. This function and related 

 protem synthesis approach a normal rate only when the mitotic rate slows 

 down. 



in. Enzymatically Degraded Cells, {a) Bacterial Protoplasts. Lester (1953) 

 showed that Micrococcus lysodeikticus, treated with lysozyme in a medium 

 containing concentrated sucrose, was able to incorporate leucine-C^^ into 

 protein. The incorporation was enhanced in the presence of DNAase and 

 abolished by RNAase. It seems probably that these results were obtained by 

 protoplasts, i.e., bacteria lacking their cell walls; these results have been 

 reproduced and extended with carefully prepared protoplasts (Bridoux and 

 Hanotier, 1956). 



McQuillen (1955a) has shown that intact but not lysed protoplasts of 

 B. megatherium are capable of actively synthesizing protein and nucleic acid. 

 Despite their lack of cell walls, protoplasts are capable of bacteriophage 

 multiplication, if infection is accomplished prior to the removal of the cell 

 wall (Salton and McQuillen, 1955; Brenner and Stent, 1955). They are also 

 capable of growth and division (McQuillen, 1955b) and the induced bio- 

 synthesis of enzymes, including permeases (Landman and Spigeleman, 1955; 



