SYSTEM CONTROLLING EXPRESSION OF ANTIRESTRICTION GENES ARDA AND ARDB OF INCN TRANSMISSION PLASMID PKM101 (R46)

A system regulating the expression of antirestriction genes ardA and a rdB of transmission plasmid pKM101 (R46) was studied. These phylogenet ically distant genes are involved in protecting plasmid DNA from cell restriction enzymes and adapting to a new host after conjugal transfer . The regulatory system involves two conserved upstream repeats, which flank the 5' end of ard and contain a potent promoter, and regulatory proteins ArdK and ArdR. At least one of the proteins, ArdK, can bind with the promoter and act as a suppressor. Both proteins control the e xpression of their own genes. The regulatory system was assumed to tri gger the coordinated expression of the ard genes and efficient synthes is of the Ard antirestriction proteins, which are essential to conjuga l transfer of the plasmid and its adaptation to the new host.