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J. Bacteriol., Nov 1995, 6137-6143, Vol 177, No. 21
I Suzuki, H Kikuchi, S Nakanishi, Y Fujita, T Sugiyama and T Omata
The gene (nirA) for nitrite reductase was cloned from the nonheterocystous,
filamentous cyanobacterium Plectonema boryanum. The predicted protein
consists of 654 amino acids and has a calculated molecular weight of
72,135. The deduced amino acid sequence from positions 1 to 511 is strongly
similar to the entire sequence of the ferredoxin-dependent nitrite
reductases from other phototrophs, while the remainder of the protein is
unique to the Plectonema nitrite reductase. The C-terminal portion of the
protein (amino acids 584 to 654) is 30 to 35% identical to [2Fe-2S]
ferredoxins from higher plants and cyanobacteria, with all of the four Cys
residues involved in binding of the [2Fe-2S] cluster in the ferredoxins
being conserved. Immunoblotting analysis of the extracts of P. boryanum
cells showed that the NirA polypeptide has an apparent molecular mass of 75
kDa. An insertional mutant of nirA lacked the 75-kDa polypeptide, had no
nitrite reductase activity, and failed to grow on nitrate and nitrite,
indicating that the novel nirA is the sole nitrite reductase gene in P.
boryanum and that the NirA polypeptide with the ferredoxin-like domain is
the apoprotein of the functional nitrite reductase. As in Synechococcus sp.
strain PCC7942, nirA is the first gene of a large transcription unit (>
7 kb in size) and is repressed by ammonium and derepressed simply by
deprivation of ammonium from the medium. The development of nitrite
reductase activity was, however, found to require the presence of nitrate
in the medium.
Copyright © 1995, American Society for Microbiology
A novel nitrite reductase gene from the cyanobacterium Plectonema boryanum
Department of Applied Biological Sciences, School of Agricultural Sciences, Nagoya University, Japan.
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