INTERMKOIATI- UKACTIONS IN PROTUIN SYNTHESIS 



.67 



MICROSOME PROTEIN 



Fig. 7. Time curve of transfer of 

 leucine-C" from prelabeled pH s 

 fraction to microsome protein. 



(From (22).] 



5 10 15 



MINUTES 



It has been possible to demonstrate a partial requirement for S-RNA in the 

 over-all incorporation of amino acid into protein by starting with a system con- 

 taining very litde S-RNA per se (44, 41). Addition of unlabeled S-RNA to 

 ascites microsomes plus supernatant enzymes (S4) resulted in an increased in- 

 corporation of C^*-leucine into the proteins. This is shown in table i. This effect 

 can be demonstrated only when there is little or no S-RNA already present in 

 the incorporation system. 



Less direct evidence for the participation of S-RNA in the over-all incorpora- 

 tion reaction is shown by the demonstration of a partial CTP dependence on the 

 over-all incorporation of amino acid into protein. In order to do this it is necessary 

 to remove all of the endogenous CTP. This is accomplished by centrifuging the 

 microsomes from a very dilute 15,000 g supernatant and by using a preincubated 

 pH 5 fraction plus a soluble fraction which had been treated with Dowex-i in 

 the chloride form to remove free nucleotides. The increase of incorporation in 

 the presence of CTP is indicated in table 2. 



Table i. Enhancement of inc;orporation of c"-leucine into protein 



From (44 j. 



