RNA AND CONTROL OF CELLULAR PROCESSES 129 



inside the cytoplasm, and sometimes even specificalK , I^nt tlie nature 

 ol this mechanism is obscure and mav become evident onlv after 

 fin^ther progress in biochemistry. 



Conclusions 



This is the picture I wanted to present. Let us step ])ack and 

 look at its main features. Genes, as DNA, carry information about 

 the amino acid sequence in proteins, but also determine the rate of 

 protein formation through the control of RNA production and the 

 stage in the cell life when the formation should occur. While the 

 first lies entirely in the gene, the two other qualities emerge as an 

 interaction with the rest of the cell or the organism. 



There is a flow of information from the nucleus to the cytoplasm 

 and this flow can be explained in chemical terms. RNA is synthe- 

 sized on the genes, to carrv the information into the cytoplasm. It 

 is the rate of RNA svnthesis which is the main determining factor 

 for the amount of enzyme or protein to be produced in the cell. This 

 rate depends on gene activity— all genes are not active at all times. 

 In order for the cell to function norm all v, certain information should 

 be fed back to the nucleus. It is not probable that RNA, once in- 

 corporated in the ribosomes, could serve as a feedback directly. 

 It must be a product of RNA action which informs the nucleus about 

 the state of RNA in the cell. This could be the protein produced 

 by RNA. But protein molecules themselves are large, moving 

 through the cytoplasm sluggishlv and being easily absorbed on 

 specific structures. Then the product of enzyme action must be the 

 feedback signal. This is usually a small molecule, present in larger 

 amounts than either RNA or enzyme. This molecule can easily dif- 

 fuse back to the nucleus and the probability that it will meet the 

 gene is high. 



But such a simple relationship is not sufficient to control all pro- 

 tein productions. Some proteins mav be devoid of enzyme activity, 

 others may be required to initiate new metabolic reactions. In these 

 cases, there would be no ordinary feedback of the product of gene 

 action, but a more complicated condition, where the nucleus is in- 

 formed of a particular state of the cell or organism. This informa- 

 tion, under appropriate conditions, would activate genes to produce 

 RNA for building of new proteins and enzymes. Again, the signal 



