Regulation of ammonium/methylammonium transport by ammonium in the cyanobacterium Anabaena variabilis

The ammonium transport system of Anabaena variabilis Kütz ATCC 29413 was studied with regard to its repression and derepression using [¹⁴C]-methylammonium as an analogue for ammonium. Whereas N₂-grown cells showed an active ammonium transport system, the latter was repressed in ammonium-grown cells. Repression of the ammonium transport system by ammonium did not require ammonium assimilation or de novo protein synthesis, suggesting that ammonium itself was the repressor signal. The derepression of the ammonium transport system however, required de novo protein synthesis and glutamine synthetase activity.