Global transcriptional regulator KorC coordinates expression of three backbone modules of the broad-host-range RA3 plasmid from IncU incompatibility group.

摘要

The broad-host-range conjugative RA3 plasmid from IncU incompatibility group has beenudisolated from the fish pathogen Aeromonas hydrophila. DNA sequencing has revealed audmosaic modular structure of RA3 with the stabilization module showing some similarityudto IncP-1 genes and the conjugative transfer module highly similar to that from PromAudplasmids. The integrity of the mosaic plasmid genome seems to be specified by its regulatoryudnetwork. In this paper the transcriptional regulator KorC was analyzed. KorCRA3 (98udamino acids) is encoded in the stabilization region and represses four strong promotersudby binding to a conserved palindrome sequence, designated OC on the basis of homologyudto the KorC operator sequences in IncP-1 plasmids. Two of the KorCRA3-regulated promotersudprecede the first two cistrons in the stabilization module, one fires towards replicationudmodule, remaining one controls a tricistronic operon, whose products are involved in theudconjugative transfer process. Despite the similarity between the binding sites in IncUudand IncP-1 plasmids, no cross-reactivity between their KorC proteins has been detected.udKorC emerges as a global regulator of RA3, coordinating all its backbone functions: replication,udstable maintenance and conjugative transfer.