COMPARATIVE COMPUTER-ANALYSIS OF THERMODY NAMIC PARAMETERS OF THE SECONDARY STRUCTURE OF TRANSFER-RNAS

Thermodynamic parameters of the cloverleaf secondary structure of tRNA s of Several major taxons (archaebacteria, eubacteria, eukaryotes, chl oroplasts, and mitochondria) were subjected to computer analysis. The distribution of free-energy values was close to normal in all groups ( except for the mitochondrial tRNA). In the organisms existing under ex treme environmental conditions, the stability of the tRNA secondary st ructure was higher. Comparative analysis of the frequency of ''quasi-c omplementary'' GU pairs in stems of randomly generated and real sequen ces demonstrated preferential fixation of such pairs in the contexts w ith the most favorable thermodynamic parameters. Noncanonic pairs in t RNA stems set limits on the presence of highly mutable CG dinucleotide s. Moreover, the effect of noncanonic pairs other than GU on the frequ ency of such dinucleotides is far more pronounced than that of GU pair s.