Figure 6. Proposed model of the nitrate assimilation regulation in P. denitrificans.

The model describes the regulatory cascade controlling expression of nitrate assimilation nas genes by the ntrBCYX gene cluster in response to ammonium availability and by the nasTS genes for nitrate control. Levels 1 and 2 include regulatory mechanisms that control transcription of the nas genes, whereas level 3 involves a control on the translation of the Nas proteins. A circle with a plus symbol means activation of the transcription and a circle with the capital letter A indicates transcription antitermination.