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 organisms spanning from prokaryotes to eukaryotes were collected from the DNA data banks and translated first, they were aligned next, then evolutionary distances were computed, and molecular phylogeny was finally estimated. The results of the alignment reveal that functionally important regions of glutamine synthetase have been evolutionarily more conserved than the remaining regions. The evolutionary distances computed also show that the rate of synonymous substitution is higher than that of nonsynonymous substitution. These are well in accordance with the neutral theory of molecular evolution. Besides, the molecular phylogeny obtained shows that the origin of glutamine synthetase gene is much earlier than the divergence between eukaryotes and prokaryotes, suggesting that the gene is one of the oldest genes functioning now.