CLONING, SEQUENCING, AND REGULATION OF THE GLOBAL NITROGEN REGULATOR GENE NTCA IN THE UNICELLULAR DIAZOTROPHIC CYANOBACTERIUM CYANOTHECE SPSTRAIN BH68K
Rl. Bradley et Kj. Reddy, CLONING, SEQUENCING, AND REGULATION OF THE GLOBAL NITROGEN REGULATOR GENE NTCA IN THE UNICELLULAR DIAZOTROPHIC CYANOBACTERIUM CYANOTHECE SPSTRAIN BH68K, Journal of bacteriology, 179(13), 1997, pp. 4407-4410
In cyanobacteria, ammonium represses expression of proteins involved i
n nitrogen fixation and assimilation. The global nitrogen regulator ge
ne ntcA encodes a DNA-binding protein, NtcA, that is a transcriptional
activator of genes subject to nitrogen control. We report the cloning
and sequencing of the ntcA gene from a nitrogen-fixing unicellular cy
anobacterium, Cyanothece sp. strain BH68K. The gene comprises 678 nucl
eotides, and the deduced NtcA protein contains 226 amino acids with a
predicted molecular weight of 25,026. In addition, ntcA mRNA levels we
re measured in cells grown under different nitrogen regimes. Under nit
rogen-fixing conditions, ntcA transcripts were weakly expressed. Furth
ermore, ntcA expression was diminished or inversely proportional to ni
fHDK expression. Conversely, ntcA expression increased in nitrate-grow
n cells, and a concentration-dependent increase was seen in ammonium-g
rown cells up to 1 mM NH4Cl. These results indicate that ntcA is invol
ved more in nitrogen assimilation than in nitrogen fixation and also i
mply that the rhythmic expression of ntcA and nifHDK transcription may
be under the control of a circadian clock.