Sequence, identification and effect on conjugation of the rmoA gene of plasmid R100-1

The rmoA gene was recently identified from two partially overlapping sequences corresponding to a region close to the end of the tra operon of plasmid R100. Its putative amino acid sequence showed strong homology to the Hha protein of Escherichia coli and YmoA protein of Yersinia enterocolitica, which are modulators of gene expression in response to environmental stimuli. We have cloned the rmoA gene from plasmid R100-1 in pUC19 and obtained the complete nucleotide sequence, which was previously published only partially and may have contained some mistakes. The rmoA gene product has been identified in radiolabelled minicells as a protein of the predicted molecular mass. The wild-type rmoA gene of plasmid R100-1 has been mutated by gene replacement and its effect on the efficiency of conjugation has been analysed. When grown in LB medium, cells harbouring R100-1 plasmid with a disrupted copy of rmoA showed a five-fold increase in conjugation frequency compared to cells harbouring R100-1 plasmid with the wild-type rmoA gene, grown in the same conditions. When cells were grown in NaCl-free LB medium they showed a 50-fold increase in conjugation frequency.