Molecular Evolution © by Springer-Verlag • 1979 Evolution of Methionine Initiator and Phenylalanine Transfer RNAs

Summary. Sequence data from methionine initiator and phenylalanine transfer RNAs were used to construct phylogenetic trees by the maximum parsimony method. Although eukaryotes, prokaryotes and chloroplasts appear elated to a common ancestor, no firm conclusion can be drawn at this time about mito-chondrial-coded transfer RNAs. tRNA evolution is not appropriately described by random hit models, since the various regions of the molecule differ sharply in their mutational fixation rates. 'Hot ' mutational spots are identified in the T~C, the amino acceptor and the upper anticodon stems; the D arm and the loop areas on the other hand are highly conserved. Crucial tertiary interactions are thus essentially preserved while most of the double helical domain undergoes base pair interchange. Transitions are about half as costly as transversions, suggesting that base pair nterchanges proceed mostly through G-U and A-C intermediates. There is a preponderance of replacements starting from G and C but this bias appears to follow the high G + C content of the easily mutated base paired regions