324 A. C. R. Dean and Sir Cyril Hinshelwood 



Pardee, Paigen and Prestidge have shown that the RNA of 

 Escherichia coli can be separated by electrophoresis into two 

 fractions. The major fraction has a high molecular weight and 

 is firmly bound to protein. The other fraction has a molecular 

 weight of less than 5000 and a higher electrophoretic mobility, 

 apparently a different base composition, and seems to be less 

 firmly bound to protein. 



The RNA content of cells in which the synthesis of protein is 

 inhibited by chloramphenicol, increases on incubation and the 

 new RNA is similar in electrophoretic mobility and firmness 

 of binding to the low molecular weight component of Pardee, 

 Paigen and Prestidge. In base composition, however, it 

 resembles the major fraction and seems to differ from the 

 normal minor component in size. Neidhardt and Gros (1957) 

 have shown that the RNA formed in the presence of chlor- 

 amphenicol and in the absence of concomitant protein synthe- 

 sis in Esch. coli is extremely unstable and breaks down when 

 the cells are subsequently incubated in the absence of the 

 drug. The resulting fragments, however, are resynthesized 

 into RNA when chloramphenicol and a source of energy are 

 added. In a similar sort of study Hahn and co-workers (1957) 

 find that cells of Esch. coli B/r, whose protein synthesis is 

 inhibited by chloramphenicol, accumulate several times the 

 amount of intracellular nucleic acids contained in log phase 

 cells before the onset of chloramphenicol-induced bacterio- 

 stasis. On removal of the drug, the bacteria recover and much 

 of the excess of nucleic acids is ejected before growth and 

 multiplication are resumed. It seems that an imbalanced 

 synthesis of normal nucleic acids takes place under the 

 influence of chloramphenicol rather than the formation and 

 elimination of abnormal polynucleotides. 



That RNA preformed in the absence of protein synthesis 

 participates neither in subsequent protein synthesis nor in 

 induced enzyme (p-galactosidase) formation was concluded by 

 Ben-Ishai (1957). 



It is generally believed that DNA is a more stable compon- 

 ent of the cell than RNA. In the experiments of Neidhardt 



