EVOLUTION OF GLUTAMINE-SYNTHETASE GENES IS IN ACCORDANCE WITH THE NEUTRAL THEORY OF MOLECULAR EVOLUTION

Evolution of glutamine synthetase gene is discussed on the results of DNA sequence analysis of the gene. Thirty DNA sequences of various org anisms spanning from prokaryotes to eukaryotes were collected from the DNA data banks and translated first, they were aligned next, then evo lutionary distances were computed, and molecular phylogeny was finally estimated. The results of the alignment reveal that functionally impo rtant regions of glutamine synthetase have been evolutionarily more co nserved than the remaining regions. The evolutionary distances compute d also show that the rate of synonymous substitution is higher than th at of nonsynonymous substitution. These are well in accordance with th e neutral theory of molecular evolution. Besides, the molecular phylog eny obtained shows that the origin of glutamine synthetase gene is muc h earlier than the divergence between eukaryotes and prokaryotes, sugg esting that the gene is one of the oldest genes functioning now.