The par region of pSC101 affects plasmid copy number as well as stability

Summary The par locus is a segment of pSC101 that has been identified as a cis ‐acting determinant of plasmid stability. We show that par also determines copy number and must, therefore, play a role in plasmid replication. The segregation defect, but not the copy‐number reduction, of par ‐ replication origins is completely suppressed by a short sequence from the bacteriophage lambda gene O which is present in plasmid pKO‐4. Thus, replication and segregation functions are separable from each other.