The Protein Text 



89 



protein-synthesizing template (RNA), the amino acids polymerize to form 

 protein; when lined up on DNA, the nucleotide portions polymerize to form 

 RNA (Fig. 5). 



If this is correct, an obvious conclusion follows. Since omission of a single 

 amino acid stops RNA synthesis, the RNA-fonning mechanism must distinguish 

 not four, but a minimum of twenty different kinds of items. But since the 

 product contains only four, the RNA in general must contain less information 

 than the template that made it. Several nucleotides in DNA must be involved 

 in selecting a single nucleotide of RNA. Since the template must contain more 

 information than the product, RNA cannot be the template for itself; i.e. it 

 cannot be self-replicating. There is an important exception to this statement. 



AMINO ACIDS 



NUCLEOTIDES 



TEMPLATE 



Fig. 5. Schematic representation of the synthesis of RNA and protein from 

 common precursors (see text). The nature of the template is presumed to deter- 

 mine whether the aligned precursors polymerize to produce protein or RNA. 



If the information in the template is reduced below a certain level, it is possible 

 to obtain a product identical to the template itself. The formalization is as 

 follows. 



While in process of formation, the RNA molecule can be visualized as a 

 sequence of nucleotides to which amino acids are attached (Fig. 5). Before 

 removal of amino acids on polymerization the informational content of the 

 'proto-RNA,' of length n, is n loga 20. After removal of the amino acids the 

 information content is reduced to n logg 4. If restrictions of some kind exist 

 on the number of combinations allowed, the number possible for 'proto-RNA' 

 will be reduced to b[n loga 20]; (b < 1). Such restrictions on 'proto-RNA' will 

 result in less severe restrictions on the RNA itself, since in general one con- 

 figuration of RNA can correspond to numerous different configurations of 

 'proto-RNA'. Therefore, if there are 20*" possible configurations of 'proto- 

 RNA', RNA itself has 4*^" possible configurations available (1 > c > b). 



The information content of RNA will equal that of 'proto-RNA' 



bn log2 20 = en log2 4 



(5 



when 1 > c^ 2.166. Since the information content of 'proto-RNA' is now 

 the same as that of RNA, an RNA template could, fonnally, be self-replicating. 

 It is now possible to reconcile the genetic and biochemical facts outlined 

 above. Assume that the synthesis of RNA proceeds in two steps. At the first 

 step, a strand of RNA is synthesized using a DNA template. Information is 

 thus transferred from DNA to RNA. The next step is supposed to occur in 

 the cytoplasin. RNA material is added to the nuclear-synthesized RNA, but 

 in a manner which does not add to the informational content. A model for 



