BamD is predicted to be rich in tetratricopeptide repeat structure, a feature it shares with the mitochondrial receptor for b-barrel proteins. BamE is needed for outer membrane integrity in E. coli, Pseudomonas aeruginosa and Salmonella enterica. Despite a high degree of sequence conservation across the major groups of proteobacteria, none of these lipoproteins have homologs in eukaryotes and thus must be absent from the machinery that assembles b-barrel proteins in mitochondria. We sought to determine if the BAM complex, like the mitochondrial SAM complex, might be modular in structure, with novel modules conferring important properties to the holo-BAM complex. Because of the ancestral link between mitochondria and a-proteobacteria, we developed methods to characterize the BAM NQDI-1 complex from Caulobacter crescentus, using native-gel electrophoresis and immunoprecipitation with an antiserum directed against the BamA subunit. After immunoprecipitation, mass spectrometry revealed the presence of BamB, BamD and Bam E subunits. In addition, the a-proteobacterial BAM complex has a novel subunit, Pal, with a characteristic OmpA-like domain that binds to the peptidoglycan layer rendering Pal immobile in the outer membrane in vivo. We suggest that this anchorage of Pal minimizes the separation between the outer and inner membrane, thereby assisting the BAM complex in accessing substrate proteins transported through the cytoplasmic membrane. Replication of the circular E. coli chromosome (R)-(+)-BAY K 8644 starts at the origin of replication, and proceeds bidirectionally to a region on the opposite side called Ter, where replication is terminated. Within the Ter region are found ten short DNA sequences, called ����Ter���� sites, which are similar but not identical. Binding of Tus, a 35 kDa trans-acting protein, to the Ter sequences blocks movement of the DNA replication complex in an orientation-specific manner: Ter sites in the permissive orientation allow the replication complex to pass, whereas Tus/Ter complexes in the non-permissive orientation block its movement.