Cloning the cyd gene locus coding for the cytochrome d complex of Escherichia coli

Two plasmids containing the two structural genes for the inner-membrane-bound cytochrome d complex (Cyd) have been isolated from the Clarke and Carbon Escherichia coli DNA bank. A 5.4-kb DNA fragment from one plasmid was subcloned in both orientations into pBR322. The promoter(s) and both genes must have been present within this fragment since the two orientations yielded similar levels of Cyd. Recombination and transduction studies indicated that the cyd gene locus had been isolated. These results demonstrate that cyd contains all the structural information for the complex. Overproduction of Cyd has yielded a visual screening procedure for plasmids bearing cyd that is unique to colored proteins like cytochromes. Colonies of E. coli bearing the cloned cyd gene are yellow-green. The cyd gene can, therefore, be used as a vehicle for detection of inserted DNA fragments.