104 CONTROL MECHANISMS IN CELLULAR PROCESSES 



different properties from RNA made in normal cells (Pardee et al., 

 1957; Hahn et al, 1957; Neidhardt and Gros, 1957; Horowitz et al, 

 1958). Chloramphenicol may have inhibited the synthesis of pro- 

 teins which either function in the formation of RNA, or which are 

 necessary to stabilize the RNA once formed. The need for a com- 

 plete set of amino acids in RNA synthesis (Gale and Folkes, 1953; 

 Pardee and Prestidge, 1956; Gros and Gros, 1958) indicates at least 

 that a protein-like structure may be needed to adapt nucleotides to 

 the template. Since amino acids function as catalysts, this would 

 mean that they are released as soon as the RNA molecule is made. 

 Wilkins (1956), however, has presented an argument against this 

 hypothesis by pointing out that the structure of DNA does not look 

 like a template for amino acids. 



An entirely different role in inheritance was attributed to RNA 

 by Haurowitz (1950), who assumed that RNA does not carry any 

 information and serves only as a backbone for the protein template, 

 keeping it in an unfolded state. Probably the strongest argument 

 against this hvpothesis is the case of tobacco mosaic virus, where 

 RNA, not protein, carries the necessary information for virus re- 

 duplication. 



Function of RNA 



Localization of RNA in Cytoplasm. What is the fate of RNA 

 when it leaves the nucleus and what is its function? RNA can be 

 found in the cell in the portion of its cytoplasm which is basophilic. 

 Garnier ( 1899 ) , who studied the properties of this cytoplasm, named 

 it "ergastoplasm." He visualized its nuclear origin and its role in the 

 production of proteins. It took many years before the basophilic 

 material was recognized as RNA (Brachet, 1941). Although a la- 

 mellar structure of the ergastoplasm was suspected by its discoverer, 

 only the electron microscope could really reveal its fine structure 

 (Porter, 1954; Palade, 1955, 1956). These authors named the ob- 

 served structures "endoplasmic reticulum," superimposing this term 

 on the old and very appropriate designation, ergastoplasm. The 

 "reticulum" consists of a svstem of cisternae, vesicles and tubules 

 with small, osmiopliilic granules associated with them. The gran- 

 ules, often called Palade's granules, after their discoverer (Palade, 

 1955), are about 160 A in diameter, stain dark with osmic acid and 

 are believed to be the seat of basophilia and of RNA. In animal cells. 



