Regulation of urea uptake by ammonia in the cyanobacteriumAnabaena doliolum

The urea uptake system was studied with regard to its repression and derepression in the cyanobacterium, Anabaena doliolum. The uptake of urea was energy-dependent and was repressed in ammonia grown cells. Repression of the urea uptake by ammonium did not require ammonium assimilation or de novo protein synthesis, suggesting that ammonium itself was the repressor signal. The derepression of the urea uptake system, however, required de novo protein synthesis and glutamine synthetase activity.