416 F. GROS 



saturate the sRNA. A rough estimate shows that the total amount of amino 

 acid bound to the sRNA (proline and tyrosine excepted) corresponds to 

 0.05 % of the dry weight of the bacterium, that is }£q to J^o of the amino 

 acid pool originating from glucose. 46 



3. State of the Ribonucleoprotein in E. coli 



In bacterial cells most of the RNA is organized into particles whose prop- 

 erties are very similar to those of the microsomes of animal cells. A few 

 years ago, Schachmann et al. i7 examined several bacterial species and found 

 that most of the RNA is present in the form of a nucleoprotein which is 

 easily sedimentable (40 S). Similar observations were made by Weibull. 48 ' 49 

 At that time, the role of divalent cations as stabilizers of the particles was 

 still unknown. The work of Tissieres and Watson, 50 and that of Roberts 

 et al. bl has now established that if the concentration of Mg ++ ions is high 

 enough, a whole series of particles can be isolated from exponentially grow- 

 ing cells of E. coli. These particles vary in size: 30 S, 50 S, 70 S, 100 S. 

 Their possible relationship is: 



2(30 S) + 2(50 5) ^ 2(70 S) ^ 100 S 



The molecular weight of 30 S is about 0.75 X 10 fi , that of 50 S is 1.8 X 10 6 . 

 The 70 S particle is composed of one 30 S plus one 50 S; 100 S is a dimer of 

 70 S. When the Mg ++ concentration exceeds 10~ 3 M there is a tendency for 

 30 S and 50 S to aggregate (70 S). When the concentration is between 10 -4 

 M and 10 -3 M, 30 S and 50 S are predominant in the crude extract. Below 

 10~ 4 M, the 30 S and 50 S particles irreversibly decompose into smaller 

 subunits. 



Fractionation of the RNA of E. coli can also be achieved by starch elec- 

 trophoresis. 4243 The fastest peak corresponds to the sRNA, the slowest 

 peak (sometimes split into two peaks) contains the "bulk RNA" and is a 

 mixture of 30 S and 50 S. 



Roberts et al., bl taking advantage of the high resolving power of activated 

 cellulose, have chromatographed crude extracts of E. coli and have obtained 

 a large number of protein peaks. The elution pattern is characteristic of 

 E. coli and is reproducible. A particular fraction, to which they applied 

 the term "ribosome," contains almost all the RNA of the cell. The ribosomes 



46 J. Mandelstam, Biochem. J. 64, 55 (1956). 



47 H. K. Schachmann, A. B. Pardee, and R. Y. St airier, Arch. Biochem. Biophys. 38, 

 245 (1952). 



48 C. Weibull, J. Bacteriol. 66, 688 (1953). 



49 C. Weibull, Exptl. Cell Research 9, 139 (1955). 



50 A. Tissieres and J. D. Watson, Nature 182, 778 (1958). 



61 R. B. Roberts, R. J. Britten, and E. T. Bolton, in "Microcomal Particles and 

 Protein Synthesis" (Washington Acad. Sci.) p. 84. Pergamon Press, London, 1958. 



