Replicating function of the RS1 element associated withVibrio choleraeCTXΦ prophage

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Abstract
The RS1 element associated with Vibrio cholerae CTX phi prophage was cloned from an E1 Tor biotype Vibrio cholerae strain. We used the recA- vaccine strain Peru-15, that lacks the target for RS-mediated site-specific integration, to show that RS1 promotes autonomous replication of a suicide vector. A linker insertion in the rstR open reading frame abolished autonomous replication in Peru-15 but not in a strain containing an RS1 in the chromosome. An AT-rich region containing cis-acting elements involved in autonomous replication was identified by deletion. This region was sufficient to support autonomous replication in a strain containing an RS1 in the chromosome. DNA sequence analysis of a region present in RS1 and not RS2 revealed the presence of putative binding sites for host proteins involved in plasmid replication. These results indicate that RS1 contains a replicon distinct from RS2 which could be involved in replicative recombination events associated with tandem amplification of the CTX element.