期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：1993
卷号：90
期号：7
页码：3009-3013
DOI：10.1073/pnas.90.7.3009
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：We performed molecular phylogenetic analyses of glutamine synthetase (GS) genes in order to investigate their evolutionary history. The analyses were done on 30 DNA sequences of the GS gene which included both prokaryotes and eukaryotes. Two types of GS genes are known at present: the GSI gene found so far only in prokaryotes and the GSII gene found in both prokaryotes and eukaryotes. Our study has shown that the two types of GS gene were produced by a gene duplication which preceded, perhaps by > 1000 million years, the divergence of eukaryotes and prokaryotes. The results are consistent with the facts that (i) GS is a key enzyme of nitrogen metabolism found in all extant life forms and (ii) the oldest biological fossils date back 3800 million years. Thus, we suggest that GS genes are one of the oldest existing and functioning genes in the history of gene evolution and that GSI genes should also exist in eukaryotes. Furthermore, our study may stimulate investigation on the evolution of "preprokaryotes," by which we mean the organisms that existed during the era between the origin of life and the divergence of prokaryotes and eukaryotes.
