An origin of transfer (oriT) is a short sequence (up to 500 bp) that is necessary for transfer of the DNA that contains it from a bacterial host to recipient during bacterial conjugation. The oriT is cis-acting — it is found on the same DNA that is being transferred, and it is transferred along with the DNA. The origin of transfer consists of three functionally defined domains: a nicking domain, a transfer domain, and a termination domain.
At the beginning of conjugation of plasmids, a multi-protein complex called the relaxosome assembles around the oriT, with each individual protein binding at specific sites on the oriT. A relaxase (one of the proteins of the relaxosome) nicks the plasmid at the nic site of the oriT, catalyzing a trans-esterification reaction that transfers the 5' end of the DNA at the nic site to a tyrosine residue on the relaxase. Relaxase then moves in the 5' to 3' direction on the plasmid, unwinding the DNA in a helicase-like fashion, until it comes a full circle back to the oriT where the relaxase recognizes a termination domain that causes it to dissociate from the DNA.
References
- Byrd D. R., Matson S. W., 1997. "Nicking by Transesterification: The Reaction Catalysed by a Relaxase." Molecular Microbiology 25:6, 1011-1022
- Fu Y. H. F., Tsai M. M., Luo Y., Deonier R. C., 1991. "Deletion Analysis of the F Plasmid ori-T Locus." Journal of Bacteriology 173:3, 1012-1020
- Guasch, et al., 2003. "Recognition and processing of the origin of transfer DNA by conjugative relaxase TrwC." Nature Structural Biology Vol. 10 No. 12, 1002-1010.
- Howard M. T., Nelson W. C., Matson S. W., 1995. "Stepwise Assembly of a Relaxosome at the F Plasmid Origin of Transfer." Journal of Biological Chemistry 270:47, 28381-28386
- Lanka E., Wilkins B. M., 1995. "DNA Processing Reactions in Bacterial Conjugation." Annual Reviews in Biochemistry 64:141-169