430 F. GROS 



sRNA and finally the pRNA. Similar results have been obtained with E. 

 coli labeled with P 32 . 124 



The kinetics of incorporation of the precursors in the steady state and 

 the way the radioactivity in the RNA is distributed after "pulse" experi- 

 ments, suggest that the membrane RNA could be a precursor of the other 

 fractions of the RNA in the cell. 



Unfortunately it is not known with certainty whether the RNA which 

 is found in membrane preparations is a chemically distinct entity and 

 whether the relationship between the "RNA forming system" and the cyto- 

 plasmic membrane is fortuitous or not. 



g. Free Polymerized RNA as a Precursor of the Ribonucleoproteins 



After addition of P 32 to a growing culture of E. coli the RNA fraction 

 labeled most rapidly corresponds to an RNA of high molecular weight, free 

 or combined with a small amount of protein. This "free" RNA can be dis- 

 tinguished from the microsomal RNA of the bacteria, since the radioactiv- 

 ity precipitable from this fraction with trichloroacetic acid sediments half 

 as rapidly as the bulk of the ribonucleoprotein (80 S particles). 51 Kinetic 

 studies suggest that this special RNA fraction could be a precursor of the 

 ribosomes. Indeed, synthesis of RNA by E. coli in the presence of chlor- 

 amphenicol might merely represent an accumulation of this precursor. 



It is therefore probable that bacterial RNA is first synthesized in a free 

 form, before being combined to protein to constitute the normal particles 

 of the cell. 



IV. Uncoupled Synthesis of Macromolecules in Bacteria 



So far consideration has been given only to bacteria under normal condi- 

 tions of growth in order to analyze some intermediary steps in protein 

 biosynthesis. The relationship between nucleic acid and protein synthesis, 

 which is one of the main problems of this chapter can be studied more 

 appropriately in bacteria altered in their chemical composition or in their 

 ability to synthesize one particular constituent. 



This explains the large amount of work which has been devoted to the 

 uncoupled synthesis of macromolecules, or to the metabolic capacities of 

 bacteria after partial or complete destruction of their nucleic acids. 



The various conditions under which protein and nucleic acid synthesis 

 can be uncoupled will be examined first. 



1. Protein and RNA Synthesis in the Absence of DNA Synthesis 



It has been known for a long time that growth can take place without 

 cytoplasmic or nuclear division. For instance, bacteria after short exposure 



124 E. Volkin and L. Astrachan, Virology 2, 433 (1956). 



