THE SYNTHESIS OF PROTEINS 15 



periments on the kinetics of induced enzyme formation in bacterial 

 zygotes suggest that the rapidity of formation of new enzyme is far in 

 excess of the rate at which new ribosomal RNA could be synthesized. 

 The existence of a rapidly-tuming-over messenger RNA, whose syn- 

 thesis was initiated by the newly entering DNA, would account for the 

 results. (4) 5-fluorouracil brings about a rapid alteration of the pattern 

 of proteins synthesized by bacteria, before there is detectable incor- 

 poration of the analogue into ribosomal or transfer RNA. It is, however, 

 rapidly incorporated into an RNA component having the properties 

 described above. (5) Further study by Lamfrom of the hemoglobin 

 synthetic system alluded to earlier reveals that the mixing of soluble 

 components of reticulocytes from one species with ribosomes of another 

 species results in the formation of two kinds of hemoglobin, each char- 

 acteristic of the species from which the fractions were derived. This 

 suggests that not only ribosomes, but also a factor not sedimenting as 

 readily as ribosomes, has genetic determinative potentiahty. 



These findings taken together indicate that there may be an im- 

 portant step in protein synthesis, interposed between the soluble RNA- 

 amino acid and the ribosome. The ribosome may function as a rela- 

 tively non-specific platform upon which 'the true genetic message finds 

 a favorable structural framework for performing its template function. 

 It would then perhaps be the messenger RNA on the ribosome with 

 which the transfer-RNA molecules interact. The ability of certain pro- 

 tein synthetic systems to function in the absence of DNA speaks for a 

 certain degree of stability of the messenger RNA in its ribosomal locus. 

 ( For a more detailed discussion of these matters the reader is referred 

 to the reviews of Jacob and Monod, 1961, and Berg, 1961). 



References 



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 Bishop, J., Allen, E., Leahy, J., Morris, A., and Schweet, R., 1960. "Stages in 



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 Chantrenne, H., 1958. "Newer Developments in Relation to Protein Synthesis," 



Ann. Revs. Biochem. 27, 35. 

 Crick, F. H. C, 1958. "On Protein Synthesis," in "The Replication of Macromole- 



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