VII. SYNTHESIS OF RNA AND RIBOSOMES 305 



1959; Spahr and Hollingworth, 1961) or equally distributed among the 

 30S and oOS particles (Bolton, 1959). 



Deoxyribonuclease (DNase) is also present in ribosomes in a latent 

 form (Elson, 1959). 



The significance of other enzymes found in ribosome pellets is uncer- 

 tain. The pellet is apt to be contaminated by soluble protein and adsorp- 

 tion of enzyme by ribosomes is difficult to rule out. 



A major proportion of leucine amino peptidase was found associated 

 with ribosomes of both SOS and 50S. The profile of enzyme activity 

 corresponds to that of ribosomes in sedimentation analysis, ruling out 

 simple contamination of pellets (Fig. 5). This enzyme shows no latency 

 (Bolton and :\IcCarthy, 1959). 



Small traces of )8-galactosidase continue to sediment with ribosomes 

 after prolonged washing procedures (Fig. 7). Here again the activity of 

 the ribosome associated enzyme is partially latent. Acid phosphatase and 

 alkaline phosphatase have also been found in E. coli ribosomes (Cowie 

 et al, 1961). 



3. Nascent Protein 



Kinetic studies show the rapid appearance of newly incorporated 

 S^^- and C^*-amino acids in ribosomes (Fig. 8). The quantity corresponds 

 to about 0.1% of the total soluble protein, i.e., to the protein synthesized 

 in a period of about 5 seconds (McQuillen et al, 1959). In studies of the 

 synthesis of the structural protein of ribosomes care must be exercised to 

 distinguish the nascent protein, which is only transiently associated 

 with ribosomes and not destined to become a part of their structure. 



D. NUCLEIC ACID COMPONENTS 



Degradation of the 50S ribosomes by sodium dodecyl sulfate or by 

 phenol releases RNA of 16 and 23S corresponding to molecular weights 

 of 0.55 X 10" and 1.1 X 10^ The 30S ribosomes release a single com- 

 ponent of 16S (Kurland, 1960). Aronson and McCarthy report similar 

 results and describe further a progressive degradation to small units of 

 13. IS, 8.8S, and 4.4S which was brought about by heating or removal 

 of magnesium by dialysis. The 4.4S component was also found in the 

 RNA extracted from magnesium starved cells (Aronson and McCarthy, 

 1961; McCarthy and Aronson, 1961). Further evidence for small sub- 

 units of ribosomal RNA shows in X-ray analysis (Timasheff et al., 1961). 



The nucleotide composition of ribosomal RNA has been reported by 

 several authors and is given in Table II. Bacteria of different DNA 

 composition show a total ribosomal RNA composition which is quite 



