The generalization method of relationships among nucleotide sequences reveals an order in assimilation of amino acid...

A new method, generalization of relationships among the nucleotide sequences has been used to analyze divergency both within and across the families of isoaccepting tRNAs. Dendrogram, dipicting relations between tRNA sets with different amino acid specificities, presents the results of analysis. The method allowed to interpret dendrogram, as a reflection of final stage of the evolution of ambiguous molecules-adaptors to highly specific tRNAs. We have proposed a model of amino acid codons assimilation at this stage. According to the model, the final formation of specific adaptors was followed by assimilation of codon clusters (four codons, differing in the third position), the first dinucleotides of which were connected by transitions. Alternate steps along double-stranded coding DNA accompanied the establishment of tRNA sets with strict specificities. Complementary codons, to which specific adaptors were assigned at step the last, were involved into the process afterwards.