Gene organization for nitric oxide reduction in Alcaligenes faecalis S-6

norB and norC encoding the cytochrome b-containing subunit and the cytochro me c-containing subunit, respectively, of the nitric oxide reductase (NOR) in Al- caligenes faecalis S-6 were cloned and sequenced. Both NorB and NorC showed more than 40% sequence identity to the corresponding subunits of cy tochrome bc-type NORs in other denitrifying bacteria. norCB was in a gene c luster containing seven other genes; these were named dnr, orf2, orf3, norE , norF, norQ, and norD on the basis of their similarity with NOR systems in other bacteria. Potential FNR-binding sites were present in front of norCB , norEF, and/or orf2/orf3, suggesting that most of these genes are regulate d simultaneously by an FNR-related protein. NorB and NorC proteins produced in the membrane fraction in Escherichia coli showed no enzyme activity, pr obably due to lack of NorQ and NorD, which appear to perform some essential function for activation of the NorB-NorC complex in the recombinant E. col i.