Origin of transfer

[13] Due to its important role in initiating bacterial conjugation, the oriT is both an enzymatic substrate and recognition site for the relaxase proteins.

[4][14] Relaxase enzymes, otherwise known as DNA strand transferases part of the relaxosome complex, catalyze a strand- and site-specific phosphodiester bond cleavage at the nicn site and are specific to each plasmid.

[17] This reaction is a trans-esterification, which produces a nicked double-stranded DNA with the 5' end bound to a tyrosine residue in the relaxase.

[22] One of the main problems in using bacterial conjugation in genetic engineering is that certain selectable markers on the plasmids generate bacteria that have resistance to antibiotics like ampicillin and kanamycin.

[23] The interaction between the DNA oriT and relaxase enables antimicrobial resistance via horizontal gene transfer (Figure 1).

[3] A 2017 study on MGIs revealed that they are able to integrate themselves into the genome of the receiving bacterial cells by themselves via int, a gene that codes for the integrase enzyme.

Figure 1 ▲ Region of oriT sequence on plasmid DNA .
Figure 2 ▲ Two bacterial cells undergoing bacterial conjugation . (1) relaxase and helicase bind to the plasmid ( F-factor ) at the origin of transfer ( OriT ). Helicase unwinds the plasmid DNA and relaxase attaches to the transfer DNA strand. (3) Relaxase carries the transfer DNA strand through the pilus connecting the two bacterial cells. (4) The remaining strand is rewound with a complementary strand of DNA. (5) Relaxase joins the two ends of the transfer DNA into a circular plasmid . (6) Relaxase detaches from the plasmid. (7) New plasmid DNA is rewound with a complementary strand of DNA.