Nucleotide sequence of the partition locus of Escherichia coli plasmid pSC101.

We report here the sequence of a 375-bp EcoRI-AvaI DNA fragment that previously has been shown to contain a locus (termed partition or par) responsible for stable maintenance of the pSC101 plasmid in growing cell populations. The DNA sequence of the par region encodes no obvious proteins and contains no segments having the structural characteristics of transcriptional or translational start signals. However, segments of the par locus appear capable of forming regions of intra-strand secondary structure, one of which resembles a rho-independent transcription terminator. Computer analysis shows regions within par that have homology with sequences found near the origin of replication of the Escherichia coli chromosome and of the pBR322 and ColE1 plasmids. The par sequence homology in the pBR322 and ColE1 plasmids maps in the vicinity of sites that interact with the E. coli replication factor Y and accomplishes initiation of DNA synthesis on single-strand templates.