38. BIOSYNTHESIS OF PROTEINS IN BACTERIAL CELLS 417 



are in fact the "microsome" fraction free of cytoplasmic proteins and phos- 

 pholipids. 



The chemical composition of the particles in E. coli, prepared by differ- 

 ential ultracentrifugation is that of a pure ribonucleoprotein containing 63 % 

 of RNA and 37% of protein. The "RNA particle" is highly polymerized 

 with a molecular weight between 500,000 and 1,000,000. Its properties have 

 been studied by Doty 52 ' 53 and more recently by Watson et al. bi 



The protein fraction of the particle constitutes a chemically well-defined 

 class or entity distinct from other proteins. It contains very little cystine, 51 

 and its content in methionine and aspartic acid is lower than in most of 

 the other proteins of E. coli, whereas its content of glutamic acid, alanine, 

 glycine, and lysine is higher. 



No enzymic activity other than ribonuclease 55 can be detected in purified 

 particles from E. coli, b0 ' 51 in contrast to the situation usually found in 

 cytoplasmic granules of bacteria which contain respiratory enzymes and 

 the systems involved in oxidative phosphorylation. 56 " 58 



Such granules probably contaminate the preparations of cell membranes 

 made by osmotic lysis of bacterial protoplasts, 48, 49 in which various anabolic 

 processes can be shown to occur. 



4. State of the DNA in Bacteria 



Little is known about the organization of the DNA in the bacterial cell. 

 Bacteria contain a "nuclear material" ("nuclear bodies," "chromatinic 

 bodies") inside which all the DNA is localized as was shown by the early 

 work of Piekarski, 59 Robinow 60 and Boivin et al. 61 The question whether 

 this nuclear material is a true nucleus or a set of chromosomes is still under 

 discussion by cytologists. 62 



E. coli and Bacillus megaterium during exponential growth have an aver- 

 age number of 3 haploid chromosomes (or nuclei) per cell. This number 



52 B. D. Hall and P. Doty, in "Microsomal Particles and Protein Synthesis" (Wash- 

 ington Acad. Sci.), p. 27. Pergamon Press, London, 1958. 



53 P. Doty, H. Boedtker, J. R. Fresco, R. Haselkorn, and M. Litt, Proc. Natl. Acad. 

 Sci. U. S. 45, 482 (1959). 



84 J. D. Watson, Personal communication (1959). 



55 D. Elson, Biochim. et Biophys. Acta 27, 216 (1958). 



56 A. Tissieres, Nature 174, 183 (1954). 



57 A. Tissieres and E. C. Slater, quoted by E. C. Slater, Proc. 3rd Intern. Congr. 

 Biochem., Brussels, 1955 p. 264 (1956). 



58 R. Y. Stanier, I. C. Gunsalus, and C. F. Gunsalus, J. Bacteriol. 66, 543 (1955). 



59 G. Piekarski, Arch. Mikrobiol 8, 428 (1937). 



60 C. F. Robinow, J. Hyg. 43, 413 (1944). 



61 A. Boivin, R. Vendrely, and R. Tulasne, Bull. acad. natl. med. (Paris) [3] 131, 2 

 (1947). 



62 E. T. Spooner and B. A. D. Stocker, "Bacterial Anatomy," 6th Symposium Soc. 

 Gen. Microbiol. Cambridge Univ. Press, London and New York, 1956. 



