2001 Fiscal Year Final Research Report Summary
Studies on the physiological roles of the glnB genein cyanobhacteria.
| Project/Area Number |
11640646
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
植物生理
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| Research Institution | Nagoya University |
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Principal Investigator |
OMATA Tetsuo Graduate School of Bioagricultural Sciences, Nagoya University, Professor, 大学院・生命農学研究科, 教授 (50175270)
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| Project Period (FY) |
1999 – 2000
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| Keywords | Nitrate ssimilation / Regulation / Ammonium assimilation / Glutamine synthetase / glnB / PII protein / Phosphorylation / 2-oxoglutarate |
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| Research Abstract |
The glnB gene product (PII protein) is known to regulate the activity of glutamine synthetase at both trariscriptional and post-translational levels in enteric bacteria, but its role in plants and cyanobacteria was unclear. The aim of this study was to make clear the physiological functions of GlnB in cyanobacteria. The major findings of this study are as follows ;
1. Involvement of GlnB in the ammonium-promoted, post-translational regulation of nitrate assimilation activity was verified in both Synechococcus PCC7942 and Synechocystis PCC6803. We further showed in Synechococcus PCC7942 that both transport and reduction of nitrate are inhibited by ammonium in an GlnB-dependent manner.
2. Cyanobacterial GlnB is known to be modified by phosphorylation at Ser49 according to the changes in the nitrogen status of the cell. Cells having mutated GlnB with either Ala or Glu at position 49, however, showed normal response to ammonium, demonstrating that phosphoryla tion of GlnB at Ser49 has little to do with the ammonium-promoted inhibition.of nitrate assimilation.
3. Growth of a glnB deficient mutant of Synechocystis PCC6803 was impaired under high light conditions at late logarithmic phase of growth, indicating that GlnB is involved in adaptive response of the cyanobacterium to high light conditions.
4. Ammonium is known to downregulate transcription of the genes related to nitrogen assimilation, involving the Crp-type protein NtcA as the regulator. Although GlnB has been supposed to have nothing to do with the transcriptional regulation of these genes, inactivation of glnB in Synechocystis PCC6803 resulted in high-level expression of glutamine synthetase (GS) activity. We found that expression level of the GS genes (glnA and glnN) was specifically elevated in the mutant. The results suggested that GlnB specifically regulates the GS genes among the genes controlled by NtcA.
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