The occurrence of eukaryotic type III glutamine synthetase in the marine diatom Chaetoceros compressum |
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Authors: | Kinoshita Shigeharu Isu Sayaka Kaneko Gen Yamada Hiroshi Hara Takeya Itoh Yasuo Watabe Shugo |
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Institution: | aDepartment of Aquatic Bioscience, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo 113-8657, Japan;bCentral Laboratory Marine Ecology Research Institute, Iwawada, Onjuku, Isumi-gun, Chiba 299-5105, Japan |
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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 Chaetoceros compressum. 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. |
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Keywords: | GS GSIII Molecular evolution Plankton |
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