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Bacterial conjugation is the process of plasmid DNA transfer from a donor cell to a recipient cell. This process is mediated in F-like plasmids by proteins expressed by the tra operon. The relaxosome forms at oriT (origin of transfer), where the nicking and unwinding of a single-stranded copy of the plasmid begins, and the transferosome forms a transmembrane pore through which the DNA is transferred.

TraM is a tetrameric relaxosomal protein which binds to 3 sites at oriT–sbmA, sbmB, and sbmC. TraD is an inner membrane protein of the transferosome that is homologous to FtsK/SpoIIIE hexameric ATPases. The interaction between the C-terminal tail of TraM and TraD is essential for high conjugation efficiency. The structural basis of this interaction is revealed by the crystal structure of F TraM58-127 in complex with TraD711-717. Electrostatic complementarity is a key feature of TraM-TraD interaction, which includes the TraM K99-TraD D715 and TraM R110-TraD F717 C-terminal carboxylate interactions. An additional feature is the fit of the phenyl side chain of F717 into a hydrophobic pocket. The importance of the TraD C-terminal tail for binding to TraM was tested with a pulldown assay comparing TraD constructs with and without a C-terminal truncation of 8 residues. In vivo assays confirmed the role of the C-terminal tail and its individual residues in conjugation.