ORGANIZATION OF THE NAR GENES AT THE CHLZ LOCUS

The two membrane-bound respiratory nitrate reductases of Escherichia c oil are encoded by distinct operons at two different loci, chlC and ch lZ, on the chromosome. The chlZ locus includes a narK homologue, narU, encoding a nitrite extrusion protein, and narZYWV encoding nitrate re ductase Z. No apparent homologue to the narXL operon has been found. H omology between narU and narK on the one hand and narZYWV and narGHJI on the other hand is limited to the coding regions.