The pSC101 par locus alters protein-DNA interactions in vivo at the plasmid replication origin.

We report here direct evidence that mutations in the par locus affect protein-DNA interactions in vivo at the replication origin of plasmid pSC101. Concomitant with par-mediated plasmid stabilization, two sites in the origin region show an altered methylation pattern as detected by in vivo footprinting with dimethyl sulfate. One site is located near an integration host factor-binding sequence adjacent to the first of three direct repeats known to be involved in the initiation of pSC101 replication; the second site is within the third direct repeat.