398 RICHARD SCinVKKT AND JOHN lUSHOP 



data). Tims, in this extivmo case, assuming the ex])eriments ai'e testing 

 RNA turnover adequately, tliere is no evidence for any kind of infoima- 

 tion turnover. 



The studies with cell-free systems have attempted to study this 

 question further, and also to change the "information" in reticulocyte 

 rihosomes, even though this might not occur in the intact cell. Lamfrom 

 (1961) incubated the rihosomes of rabbit or sheep reticulocytes with 

 enzyme fractions from rabbit or sheej) supernatants, and concluded that 

 the hemoglobin tj^pe synthesized was partly a function of the species 

 from which the ribosomes were derived. However, some hemoglobin 

 corresponding to the species from which the soluble fraction was derived 

 was also found. It was concluded that the pH 5 precipitate was inactive 

 in this respect, and that the ability to change the specificity of the 

 ribosomes was found in tlie pH 5 supernatant. Kruh et al. (1961) 

 described a rather different situation. Using ribosomes and soluble frac- 

 tions derived from the reticulocytes of the rabbit and the guinea pig, 

 considerable synthesis of the heterologous type of hemoglobin was 

 observed when the ribosomes of one species were incubated with the 

 pH 5 precipitate of the other. Thus, Kruh et al. (1961) concluded that 

 soluble fractions could change the type of hemoglobin synthesized, but 

 the opposite enzyme fraction was effective. Bishop et al. (1961), using 

 reticulocytes of the rabbit and the mouse, incubated the ribosomes of 

 one species with a mixture of the ribosomal supernatants of both species, 

 and found that the hemoglobin synthesized corresponded to the species 

 which provided the ribosomes. It is possible that the use of mixed 

 supernatants resulted in the failure of a potential specificity change to 

 be expressed if greater affinity existed between homologous than be- 

 tween heterologous factors. Recently, Miller and Lamfrom (1962) ex- 

 tended these studies to duck-rabbit mixtures. In this case, hemoglobin 

 corresponding to the ribosome species was synthesized, and in addition 

 radioactivity was found in a protein peak which appeared to be a hyl)rid 

 hemoglobin (composed of chains from both species). Thus, the evidence 

 for the synthesis of hemoglobin different from the ribosome species used 

 is conflicting, and further studies are required to decide whether the 

 addition of supernatant fractions from one species can result in synthesis 

 of the hemoglobin of that species when ribosomes of another species are 

 used. In addition, no evidence that RNA is involved has been presented 

 as yet. 



Another approach to the problem of infomiation transfer has been 

 to study whether it is necessary to provide sequence information to the 

 ribosome in order to synthesize hemoglobin in the cell-free system. Both 

 Ki'uh ct (tl. (1961) and Lamfrom (1961) reported that no soluble Ikmho- 



