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J. Bacteriol., Sep 1997, 5744-5750, Vol 179, No. 18
Y Harano, I Suzuki, S Maeda, T Kaneko, S Tabata and T Omata
An open reading frame (slr0899) on the genome of Synechocystis sp. strain
PCC 6803 encodes a polypeptide of 149 amino acid residues, the sequence of
which is 40% identical to that of cyanase from Escherichia coli.
Introduction into a cyanase-deficient E. coli strain of a plasmid- borne
slr0899 resulted in expression of low but significant activity of cyanase.
Targeted interruption of a homolog of slr0899 from Synechococcus sp. strain
PCC 7942, encoding a protein 77% identical to that encoded by slr0899,
resulted in loss of cellular cyanase activity. These results indicated that
slr0899 and its homolog in the strain PCC 7942 represent the cyanobacterial
cyanase gene (designated cynS). While cynS of strain PCC 6803 is tightly
clustered with the four putative molybdenum cofactor biosynthesis genes
located downstream, cynS of strain PCC 7942 was found to be tightly
clustered with the two genes located upstream, which encode proteins
similar to the subunits of the cyanobacterial nitrate-nitrite transporter.
In both strains, cynS was transcribed as a part of a large transcription
unit and the transcription was negatively regulated by ammonium. Cyanase
activity was low in ammonium-grown cells and was induced 7- to 13-fold by
inhibition of ammonium fixation or by transfer of the cells to ammonium-
free media. These findings indicated that cyanase is an ammonium-
repressible enzyme in cyanobacteria, the expression of which is regulated
at the level of transcription. Similar to other ammonium- repressible genes
in cyanobacteria, expression of cynS required NtcA, a global nitrogen
regulator of cyanobacteria.
Copyright © 1997, American Society for Microbiology
Identification and nitrogen regulation of the cyanase gene from the cyanobacteria Synechocystis sp. strain PCC 6803 and Synechococcus sp. strain PCC 7942
Department of Applied Biological Sciences, School of Agricultural Sciences, Nagoya University, Japan.
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