RNA AND CONTROL OF CELLULAR PROCESSES 99 



mal RNA (Pardee et al, 1957; Hahn et al, 1957; Neidhardt and Gros, 

 1957; Horowitz et al., 1958). Notliing is known about the function 

 of amino acids in the svntliesis, although several interesting models 

 have been proposed ( Raacke, 1958 ) . 



In broken cell preparations it has been sliown that DNA is re- 

 quired for RNA s\n thesis. RNA synthesis was specificallv stopped 

 in homogenized preparations of bacteria after enzymatic destruction 

 of DNA with deoxyribonuclease and reconstituted upon the addition 

 of bacterial DNA (Gale and Folkes, 1958). Allfrey and Mirsky 

 (1957) showed that in isolated nuclei, the incorporation of radio- 

 active precursors into RNA was reduced after the depletion of DNA 

 and restored with the addition of DNA. Later, however, equally 

 good restoration was obtained with some polvanions (Allfrev and 

 Mirsky, 1958), so that the direct role of DNA in RNA synthesis could 

 not be demonstrated. 



While intact DNA seems to be necessarv for RNA formation, a 

 simultaneous DNA replication is not necessary. When DNA repli- 

 cation was inhibited in bacteria with mustard gas or other chemicals, 

 RNA sMithesis continued (Harold and Ziporin, 1958; Kerridge, 

 1958). Mutants deficient in thvmine were unable to build new 

 DNA, but increased their RNA (Rarner and Cohen, 1958; Okazaki 

 and Okazaki, 1958). Also, in the resting cells of higher organisms, 

 DNA is normally not replicating, while RNA synthesis proceeds con- 

 tinuously. 



If DNA is responsible for RNA formation, it could be expected 

 that DNA could not function when it is being replicated. In higher 

 plant tissues, it was possible to follow by autoradiography, using P''- 

 or orotic acid C^^ as precursors, the periods when RNA and DNA 

 are synthesized in the cell (Taylor and McMaster, 1954; Sisken, 

 1959). DNA was formed for short periods during the interphase, 

 before or after mitosis, and RNA formation was low or absent during 

 these periods. In Tetrahijmena also, RNA synthesis was highest 

 after the end of the period of DNA synthesis (Prescott, 1960b). 

 In bacteria with synchronized divisions induced by temperature 

 changes, DNA and mass synthesis were more or less in phase with 

 cell division, whereas RNA synthesis was most intense durino; the 

 absence of DNA synthesis (Lark and Maal0e, 1956). McFall and 

 Stent (1959) believe, however, that the periodicity of DNA and 

 RNA production is an artefact due to the synchronization procedure. 

 In normally reproducing bacteria, it could be shown that bacteria 



