Summary:

1. The Escherichia coli msbA gene has been proposed to transport nascent core-lipid A molecules across the inner membrane (Polissi, A., and Georgopoulos, C. (1996) Mol. Microbiol. 20, 1221-1233). msbA is an essential E. coli gene with high sequence similarity to mammalian Mdr proteins and certain types of bacterial ABC transporters. Experimental evidences support the view that MsbA plays a role in lipid A and possibly glycerophospholipid transport. (J Biol Chem 1998 May 15;273(20):12466-75 Function of Escherichia coli MsbA, an essential ABC family transporter, in lipid A and phospholipid biosynthesis. Zhou Z, White KA, Polissi A, Georgopoulos C, Raetz CR PMID: 9575204, UI: 98241619)

2. cydDC operon encodes a heterodimeric ABC transporter required for assembly of cytochromes c and bd in Escherichia coli K-12. Transcriptional regulation of the cydDC operon is regulated by oxygen and alternative electron acceptors. (J Bacteriol 1997 Oct;179(20):6525-30 Cook GM, Membrillo Hernandez J, Poole RK PMID: 9335308, UI: 97474284)

3. All above genes probably are involved in the secretion of lipid A and belong to the ATP-binding transport protein family.

4. All above genes share strong similarity with each other. All have the ATP-binding domain and transmembrane region which suggest that subcellular location is integral membrane.