ASSEMBLY OF F-0 SECTOR OF ESCHERICHIA-COLI H+ ATP SYNTHASE - INTERDEPENDENCE OF SUBUNIT INSERTION INTO THE MEMBRANE

The F-0 sector of the Escherichia coli H+ transporting ATP synthase is composed of a complex of three subunits, each of which traverses the inner membrane. We have studied the interdependence of subunit insertion into the membrane in a series of chromosomal mutants in which the primary mutation prevented insertion of one of the F-0 subunits. Subunit insertion was assessed using Western blots of mutant membrane preparations. Subunit b and subunit c were found to insert into the membrane independently of the other two F-0 subunits. On the other hand, subunit a was not inserted into membranes that lacked either subunit b or subunit c. The conclusion that subunit a insertion is dependent upon the co-insertion of subunits b and c differs from the conclusion of several studies, where subunits were expressed from multicopy plasmids.