Nine unique repeating sequences in a region essential for replication and incompatibility of the mini-F plasmid.

The nucleotide sequence of a 2248 bp portion of the plasmid mini-F has been determined. This region includes the replication origin and all of the plasmid-coded information required for replication. The same region is also capable of expressing incompatibility. A striking feature of the sequence is the presence of nine 19-bp repeating units. Four of these repeats, all arranged in one direction, comprise a cluster, and the remaining five, all arranged in the opposite direction, comprise another cluster. These clusters are separated by a region of about 850 bp that encodes a hypothetical 29-kd polypeptide. This region has sequences highly homologous to those found in the origin regions of the Escherichia coli (Sugimoto et al., 1979; Meijer et al., 1979) and Salmonella typhimurium (Zyskind and Smith, 1980) genomes.