Ammonia-dependent differential regulation of the gene cluster that encodes ammonia monooxygenase in Nitrosococcus oceani ATCC 19707

Molecular analysis of the ammonia monooxygenase-encoding gene cluster in Nitrosococcus oceani revealed that the amo genes are differentially expressed from three promoters dependent on the external ammonia concentration. Whereas a distal amoRCABD operon promoter, pC1, is active only in the presence of ammonia, identified proximal amoC (pC2) and amoA (pA) sigma-70-type promoters are constitutive. Promoter region pC2 also contains a consensus sequence for binding of RpoN, usually involved in nitrogen starvation response. Additional regulation of transcript stability by anti-termination and mRNA degradation are proposed and discussed.