RNA IN THE SYNTHESIS OF PROTEINS 



genetic specificity resides in the complementary base sequences along its two 

 intertwined chains. One or both of these complementary chains must serve 

 as templates for specific RNA molecules whose genetic information again 

 must reside in specific base sequences. These RNA molecules would then 

 assume 3 -dimensional configurations containing surfaces complementary to 

 the side groups of the 20 specific amino acids. 



X-ray Studies on RNA and RNA-contaiuiug Viruses 



The direct way to test this hypothesis was to solve the RNA structure. Al- 

 ready in 1952, I had taken some preliminary X-ray diffraction pictures of 

 RNA. These, however, were very diffuse, and it was not until I returned to 

 the United States in the fall of 1953 that serious X-ray studies on RNA began. 

 Alexander Rich and I, then both at the California Institute of Technology, 

 obtained RNA samples from various cellular sources. We 9 were first very 

 encouraged that all the RNA samples, no matter their cellular origin, give 

 similar X-ray diffraction pattern. A general RNA structure thus existed. This 

 gave us hope that the structure, when solved, would be interesting. Our first 

 pictures already showed large systematic absence of reflections on the merid- 

 ian, suggesting a helical structure. But despite much effort to obtain native 

 undegraded high molecular weight samples, no satisfactory X-ray diffraction 

 pattern was obtained. The reflections were always diffuse, no evidence of 

 crystallinity was seen. Though there were marked similarities to the DNA 

 pattern, we had no solid grounds for believing that these arose from a similar 

 helical molecule. The problem whether RNA was a one- or several-chained 

 structure remained unanswered. 



We then considered the possibility that RNA might have a regular struc- 

 ture only when combined with protein. At that time (1955) there was no 

 good evidence for RNA existing free from protein. All RNA was thought 

 to exist either as a viral component or to be combined with protein in ribo- 

 nucleoprotein particles. It thus seemed logical to turn attention to a study of 

 ribonucleoprotein particles (ribosomes) since upon their surfaces protein was 

 synthesized. Our hope again was that the establishment of their structure 

 would reveal the long-sought-after cavities specific for the amino acids. 



Then we were struck by the morphological similarity between ribosomes 

 and small RNA-containing viruses like Turnip Yellow Mosaic Virus or 

 Poliomyelitis Virus. By then (1955-1956) I was back in Cambridge with 



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