ISSN:
1365-2958
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Biology
,
Medicine
Notes:
PII (glnB ) is a signal transduction protein that in Azospirillum brasilense is specifically required for nitrogen fixation. Little is known about whether and how its homologue Pz (glnZ ) participates in the regulation of cellular functions. In this study, we have shown the regulatory action of the two proteins by analysing the relevant single and double null-mutant strains. The transcription of glnZ is monocistronic, and it starts mainly from a σ54-dependent promoter, activated by NtrC. glnZ expression is dependent on the ntr system, even under conditions of nitrogen excess, and is greatly enhanced in the presence of aspartate. Pz is uridylylated in response to nitrogen limitation, like PII, although different amounts of the two proteins are synthesized. PII is required for the dephosphorylation of NtrC. Thus, in the absence of PII, the repression of nitrate assimilation is not promoted, which, in turn, leads to a high rate of ammonium excretion. Unexpectedly, PII and Pz proteins are not essential for the reversible modification of glutamine synthetase. (Methyl)ammonium transport into the cell is negatively regulated by Pz. The growth of a double-mutant strain (glnB ::kan; glnZ ::Ω ) is drastically disabled, although wild-type growth is restored by complementation with either glnB or glnZ. We conclude that PII and Pz, despite their structural similarity, are involved in different regulatory processes, except for that required for cell growth.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1046/j.1365-2958.1998.00938.x
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