THE GENETIC-CODE AND CYCLIC CODES

We proposed previously a cyclic code made of 22 triplets, which we now call the AB code. It is made up of the following chain: AUGGUGCCAUUCA AGACUAUGA. The letters A, U, C, G represent the classical symbols of t he (purine and pyrimidine) bases of the genetic cone. This chain prese nts the following features: (1) when it is in cyclic form, it begins w ith the initiation codon AUG, ends with the termination codon UGA, and it ran be read triplet after triplet by choosing 1 and only 1 represe ntative of each synonymy class in the classical degenerate genetic rod e made of 64 triplets. The chain, therefore, possesses 1 and only 1 co don for each amino-acid; (2) except for the doublet CG, triplets of th e chain begin with the 15 other possible doublets of bases (satisfying the ''wobble'' hypothesis presented by Crick); (3) it corresponds (ex cept for I base) to the ''loop'' part of the (Enothera mitochondrial G ly-tRNA; (4) it ran be modified, without loss of the properties (1) an d (2), in such a way as to have 15 bases in common with the loop part of other mitochondrial tRNA's considered as primitive, like Ala-, Pro- and Arg-tRNA; (5) it contains the most frequent triplets, but not the most rare ones, appearing in the genome of numerous species; (6) it e xhibits a coherent internal structure with respect to the molecular we ight of its triplets. This structure, also found in the loop part of m itochondrial tRNA's, contains an excess of AU bases with respect to GC bases. This fact has no explanation in the classical probabilistic mo del of the tRNA's. Therefore, we propose the cyclic AB code as a primi tive genetic structure with the essential coding properties of the pre sent genetic code.