title: The occurrence of eukaryotic type III glutamine synthetase in the marine diatom Chaetoceros compressum.
abstract: Glutamine synthetase (GS) has been described as one of the oldest functioning genes and thus a good molecular clock protein. GS is diverged into three distinct forms, type I (GSI), type II (GSII) and type III (GSIII), the last type of which is a member of the most recently discovered family among GSs and thus has been reported from a limited number of prokaryotes. In the present study, we determined the full-length sequence of GSIII from the marine diatom Chaetoceroscompressum. The 3' untranslated region of the diatom GSIII gene was composed of a polyadenylation signal followed by a poly (A)(+) tail, clearly demonstrating that its mRNA is transcribed from the eukaryotic genome. We also screened available genome databases and identified full-length GSIII sequences from 5 eukaryotic species. These eukaryotic GSIIIs specifically contained regions A-D and a long additional sequence flanking region V toward the C-terminal site, both being specific to GSIII. Phylogenic analysis revealed that eukaryotic GSIIIs are not within a monophyletic relationship with the possible occurrence of lateral gene transfer in GSIII during evolution.
authors.affiliation: Department of Aquatic Bioscience, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo 113-8657, Japan.
authors.forename: Shigeharu
authors.initials: S
authors.lastname: Kinoshita
authors.forename: Sayaka
authors.initials: S
authors.lastname: Isu
authors.forename: Gen
authors.initials: G
authors.lastname: Kaneko
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Yamada
authors.forename: Takeya
authors.initials: T
authors.lastname: Hara
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Itoh
authors.forename: Shugo
authors.initials: S
authors.lastname: Watabe