Structure and ANR-dependent transcription of the nir genes for denitrification from Pseudomonas aeruginosa.

In the denitrification gene cluster from Pseudomonas aeruginosa, an operon encoding three open reading frames (nirQ, ORF2, ORF3) was upstream of the structural gene for nitrite reductase (nirS) as a divergent transcriptional organization. A nucleotide-binding protein encoded by nirQ was 76% identical to the Pseudomonas stutzeri nirQ gene product, which was shown to be necessary for activating nitrite and nitric oxide reductases. The gene product of ORF2 was homologous to subunit III of cytochrome oxidases. The nirQ gene was transcribed under denitrifying conditions. The intergenic region of nirS and nirQ has only one binding motif for ANR, a regulatory protein for anaerobic gene expression correspond to FNR in E. coli. Complementation analyses showed that the transcription of both nirS and nirQ completely depended on ANR.