90 THE BIOSYNTHESIS OF PROTEINS 



about the nature or the state of the compound which carries it, are un- 

 fortunately not in perfect agreement with each other. Schweet et al. (1958) 

 isolated microsomes from reticulocytes and showed that the non-sediment- 

 able fraction was required together with the microsomes for amino acids to 

 be incorporated into Hb. Liver supernatant can be substituted for reticulo- 

 cytes supernatant, but liver microsomes even in the presence of reticulocytes 

 supernatant do not catalyse incorporation into Hb. This indicates that part 

 at least of the specific information must lay in the microsomes (see also 

 Allen and Schweet, 1960; Allen et al, 1960). On the other hand, Wain- 

 wright (1960) working with extracts of Neurospora reached a different 

 conclusion. The synthesis of tryptophane synthetase could be observed 

 in cell-free extracts of conidia. Mixed system containing soluble and 

 sedimentable fractions prepared from wild strain or from a mutant lacking 

 tryptophane synthetase were used. When a mutant 'particle' fraction was 

 supplemented with wild type soluble fraction, considerable tryptophane 

 synthetase was produced. Conversely, a mixture of wild type 'particles' 

 with mutant 'soluble' fraction failed to develop any detectable activity. The 

 defective component of the mutant extract has thus been located in the 

 soluble, non-sedimentable fraction. 



It is probable that in such systems, and with the progress of techniques 

 for isolation of biologically active RNA, it will soon be possible to check 

 whether the carrier of genetic information is an RNA, or else to discover its 

 nature. 



Reports from several laboratories have indicated that RNA extracted 

 from micro-organisms might cause the production of certain specific 

 proteins or might confer specific characters to homologous cells (Mina- 

 gawa et ah, 1951; Minagawa, 1955; Reiner and Goodman, 1955; Kramer 

 and Straub, 1956; Hunter and Butler, 1956; Hrubesova et al, 1959; 

 Kessler, 1957). It must be admitted that the results obtained in these 

 interesting works are not always sufficiently clear and reproducible. At 

 present, it is very difficult to evaluate them. If these observations prove to 

 be correct, they will acquire a fundamental significance comparable only 

 to bacterial transformation by DNA and to transmission of virus diseases 

 by isolated RNA. 



5. Concluding Remarks 



The participation of RNA in protein synthesis has been known for 

 twenty years. So far, a function has been clearly attributed to only one class 

 of RNA — the 'transfer RNAs' which are specific carriers of activated 

 amino acids (see p. 102). But these represent only a small fraction of total 

 RNA. The exact function of ribosomal RNA is not yet clarified. The 

 evidence for the participation of this RNA in protein synthesis remains the 

 correlation between their amount and the intensity of protein synthesis. 



