Glutamine synthetases of Corynebacterium glutamicum: transcriptional control and regulation of activity.

Regulation of glnA expression and glutamine synthetase I activity was analyzed in Corynebacterium glutamicum. Transcription is regulated by the global repressor protein AmtR, essential for derepression of glnA transcription are GlnK and uridylyltransferase, key proteins of the C. glutamicum nitrogen regulatory system. Glutamine synthetase I activity is controlled by adenylylation/deadenylylation via adenylyltransferase. The gene encoding this bifunctional enzyme, glnE, was isolated and its function was characterized by deletion analysis. Upstream of glnE, a second gene encoding a GSI-type protein in C. glutamicum was isolated. This gene, designated glnA2, forms an operon with glnE, its transcription is not regulated and neither its deletion or overexpression showed any effect. Therefore, the physiological role of glnA2 remains unclear.