Part of the outer membrane protein assembly complex, which is involved in assembly and insertion of beta-barrel proteins into the outer membrane. Constitutes, with BamD, the core component of the assembly machinery. Does not normally serve as a receptor for CdiA-EC93, the contact-dependent growth inhibition (CDI) effector of E.coli strain EC93. However if extracellular loops 6 and 7 are mutated to match the sequence of E.coli then the protein is able to act as a CdiA-EC93 receptor, conferring CDI on E.coli strains expressing the mutated BamA. The same mutations also support the delivery of CdiA-CT from strain 536 / UPEC. Part of the Bam complex, which is composed of the outer membrane protein BamA, and four lipoproteins BamB, BamC, BamD and BamE. Belongs to the BamA family.