The Presence Of MiniR1-1Plasmid Delays The Escherichia Coli Cell Division

The MiniR1-1is a derivative of R1plasmid. The genome sequence of MiniR1-1shows that the plasmid is a6316bp of circular double-stranded DNA molecule with an oriR1, origin for replication, carrying the repA gene, tap, copA, bla gene, and genes for ORF1and ORF2. The presence of MiniR1-1plasmid leads to an accumulation of the D-period cells in slowly growing Escherichia coli cells, suggesting that MiniR1-1delays cell division. We find that MiniR1-1contains8DnaA-boxes (DnaA-binding sites), and one of them is fully-matched box in the oriR1region, one with one mismatch close to the copA gene and other6with two mismatches around the plasmid. Mutagenesis analysis in the DnaA-boxes shows that the MiniR1-1effect on cell division is not due to a decrease in availability of DnaA by the titration process. A point mutation in ORF2results in a blockage of cell growth in poor medium but not in rich medium, indicating that ORF2is required for cell survival in poor medium. Microscopy analysis shows that the presence of MiniR1-1does not affect chromosome segregation. The results suggest that the presence of MiniR1-1plasmid delays cell division by an unknown process.