The transfer operon of plasmid R1 extends beyond finO into the downstream replication genes

Abstract

finO is the final gene in the 35.4 kb transfer operon of IncFI plasmid F that is known to be involved in self-conjugative transfer. The genetic region distal to finO separates the conjugation and replication control modules of IncFII plasmid R100 and carries uncharacterized genes not found in plasmid F. However, comparison of the R100 gene organization with database entries of F-like plasmids suggests its broad conservation. We determined the DNA sequence of this region of IncFII plasmid R1 and studied its transcriptional organization. We find that transcription occurs through the entire gene region spanning from finO to the 5' regulatory region of copB. The region lacks independent promoter activity and transcription is co-regulated with the adjacent transfer operon. We show that this extended transcriptional organization beyond finO is shared by plasmid R100. These findings support the hypothesis that gene products coexpressed from the finO-distal region in F-like plasmids are advantageous under some conditions when conjugative DNA is exchanged.