Partition of nonreplicating DNA by the par system of bacteriophage P1.

P1 plasmid encodes a cis-acting centromere analog, parS, and two Par proteins that together stabilize plasmids by partitioning them to daughter bacteria. We infected immune bacteria with bacteriophage lambda into which parS had been inserted. The presence of P1 Par proteins in the infected cells was found to delay the appearance of cells cured of the nonreplicating, extrachromosomal lambda-parS DNA. This stabilization of lambda-parS, approximated in a computer simulation, demonstrates that active partition by the P1 par system does not require the act of plasmid replication and can be studied in its absence.