396 mahlon b. hoagland 



5. The Nuclei 



The most extensive studies on protein synthesis in isolated calf thymus 

 cell nuclei have been carried out by Allfrey, Mirsky, and Osawa. 207 Nuclei 

 are generally difficult to isolate uncontaminated with other cell constit- 

 uents and whole cells, and in thymus cells in particular they fill a large 

 fraction of the total cell volume. It would appear to be uncertain that such 

 preparations contain only nuclei. These workers have found that such prep- 

 arations, which microscopically appear to be nuclei only, carry on an active 

 energy-dependent incorporation of C 14 -amino acids into protein and ade- 

 nine-C 14 into RN A. Treatment of these nuclei with deoxyribonuclease, which 

 removes 70-80% of the DNA, completely inactivates these incorporation 

 abilities. Ribonuclease, on the other hand, has no such effect, although it 

 was not possible to remove more than half of the RNA. Logan et al. 208 have 

 confirmed these findings using other techniques and have found similar 

 effects using rat liver nuclei. 



Another activity of thymus nuclei is the ability to carry out the oxida- 

 tive synthesis of ATP. 209 Also, this activity is lost upon deoxyribonuclease 

 treatment. A surprising finding, however, is that although the addition of 

 DNA to deoxyribonuclease-treated nuclei can restore all three of these 

 lost activities, this capacity of DNA is not specific. DNA's from other 

 sources, RNA, polyadenylic acid, and non-polynucleotides such as heparin, 

 polyethylene sulfonate, and chondroitin sulfate were all able to restore ac- 

 tivity. No explanation of this phenomenon is immediately apparent. If it 

 were possible to follow the synthesis of specific proteins in this system it 

 would be intriguing to determine whether the specificity of the process was 

 altered in the presence of these polyanions. For further consideration of the 

 synthesis of protein in nuclei and of the relationship of DNA thereto, the 

 reader is referred to the recent review by Chantrenne. 8 Further elucidation 

 of protein and RNA synthesis in nuclei is much to be desired since it should 

 shed much light on the role of DNA in directing the synthesis of specific 

 templates which will in turn carry out the extranuclear (ribosomal) syn- 

 thesis of protein. 



G. Bacterial Cell Membranes 



Cell-free bacterial preparations should be an excellent source of informa- 

 tion about the mechanism of protein synthesis. Not only are bacteria 

 homogeneous in cell type, but they make protein vigorously and offer an 

 ideal system to observe the events which occur when a cell population un- 



207 V. G. Allfrey, A. E. Mirsky, and S. Osawa, in "The Chemical Basis of Heredity" 

 (W. D. McElroy and B. Glass, eds.), p. 200. Johns Hopkins Press, Baltimore, 1957. 



208 R. Logan, A. Ficq, and M. Errara, Biochim. et Biophys. Acta 31, 402 (1959). 



209 V. G. Allfrey and A. E. Mirsky, Proc. Natl. Acad. Sci. U. S. 44, 981 (1958). 



