132 Information Storage and Neural Control 



Poliovirus Biosynthesis: Source and Time Course of Synthesis 

 of Viral Constituents 



I will now describe the source and time course of synthesis of 

 the RNA and protein of poliovirus and then discuss some new 

 evidence relating to the questions of 1) the necessity for "early" 

 protein formation prior to actual virus replication, and 2) the role 

 of poliovirus RNA as a "messenger" RNA. 



By differentially labeling the macromolecules (protein or RNA) 

 and the acid-soluble pool (amino acids or nucleotides) of HeLa 

 cells, and observing the production of poliovirus under these con- 

 ditions, it was shown that viral macromolecules were constructed 

 de novo in the infected cell from the acid-soluble pool. This was 

 true for both viral RNA and viral piotein (38, 62). 



To determine the time at which viral macromolecules were 

 synthesized relative to the maturation cycle, radioactive precursors 

 of either protein or RNA were added to the medium of infected 

 cells at various times after infection and virus purified at the end 

 of maturation (38, 63). From the isotope content of the purified 

 virus could be determined how much of the virus had been syn- 

 thesized at the time of addition of the radioisotope. Virus protein 

 and virus RNA were shown to be formed between two and one- 

 half and six hours after infection and there was very little lag 

 between the onset of formation of viral macromolecules and of 

 the whole virus. An independent confirmation of this last state- 

 ment was obtained by determining the times of formation of 

 infectious RNA (ribonuclease sensitive plaque-forming activity) 

 and of whole virus. Here the very earliest increases of infectious 

 material could be determined (the first 0.1 per cent of new virus 

 or infectious RNA). It was found that infectious RNA began to 

 increase at about 2-2.5 hours while an increase in whole virus 

 began approximately thirty minutes later. It would appear, then, 

 that for the first 2-2.5 hours of the infectious cycle the cell does 

 not make virus precursor molecules. 



The essential findings of the above experiments are borne out 

 in electron microscopic investigations of infected cells. Home and 

 Nagington (33) found evidence in electron photomicrographs of 

 circumscribed areas of apparent multiplication of protein sub- 

 units in the cytoplasm of HeLa cells, beginning about three hours 



