Investigation of the role of thecydDgene product in production of a functional cytochromedoxidase inEscherichia coli

The cydD gene is needed for the formation of a functional cytochrome d oxidase in the aerobic respiratory chain of Escherichia coli. In this paper we demonstrate that transcription from a cydA-lacZ gene fusion is not significantly affected in a cydD mutant. This, together with the finding that subunit I of cytochrome d is present in cytoplasmic membranes of a cydD mutant, rules out a role for CydD in the regulation of cytochrome d expression or the assembly of its polypeptides into the membrane. The activity of the haem d-containing catalase HP II was found to be similar in a cydD mutant and the wild-type. Therefore, if CydD has a role in haem d biosynthesis it must be in a unique step only associated with the synthesis of the haem d prosthetic group of cytochrome d.