Relaxosome

Relaxosome is the complex of proteins that facilitates plasmids during bacterial conjugation. The proteins are encoded by the tra gene in the origin of transfer, oriT, region. The most important of these proteins is relaxase, which is responsible for beginning the conjugation process by cutting at the "nic" site via transesterification. This nicking results in a DNA-Protein complex with the relaxosome bound to a single strand of the plasmid DNA and an exposed 5' hydroxyl group. Relaxase also unwinds the plasmid being conjugated with its helicase properties. The relaxosome interacts with integration host factors within the oriT.

Other genes that code for relaxosome components include TraH, which stabilizes the relaxosome's structural formation, TraI, which encodes for the relaxase protein, TraJ, which recruits the complex to the oriT site, TraK, which increases the 'nicked' state of the target plasmid, and TraY, which imparts single-stranded DNA character on the oriT site. Tra M plays a particularly important role in relaxase interaction by stimulating 'relaxed' DNA formation.

References

1. Grahn et al (2000). "Components of the RP4 Conjugative Transfer Apparatus Form an Envelope Structure Bridging Inner and Outer Membranes of Donor Cells: Implications for Related Macromolecule Transport Systems". Journal of Bacteriology. March 2000 Vol 182, No 6.