Recognition of the P1 plasmid centromere analog involves binding of the ParB protein and is modified by a specific host factor.
The P1 plasmid partition system is responsible for segregation of daughter plasmids during division of the Escherichia coli host cell. The P1-encoded elements consist of two essential proteins, ParA and ParB, and the cis-acting incB region. The incB region determines partition-mediated incompatibility and contains the centromere-like site parS. We have isolated and purified the two proteins. ParB binds specifically to the incB region in vitro. DNase I footprinting assays place a strong binding site over the 35-bp parS sequence previously shown to be sufficient for partition when the Par proteins are supplied in trans. A weaker site lies within the incB region in sequences that are important for specifying incompatibility, but are not essential for partition. Gel band retardation assays show that a host factor binds specifically to the incB sequence. The factor strongly stimulates binding of ParB. Cutting the region at a site between the two ParB binding sites yields two fragments that can bind ParB but not host factor. Thus, information for host-factor binding lies in the region determining the specificity of plasmid incompatibility. The roles of parB and the host factor in partition and the specificity of plasmid incompatibility are discussed.
D001426:Bacterial Proteins / Q000302:isolation & purification / Q000378:metabolism*; D001435:Bacteriophages / Q000378:metabolism*; D001483:Base Sequence; D004268:DNA-Binding Proteins / Q000302:isolation & purification / Q000378:metabolism*; D004926:Escherichia coli / Q000378:metabolism*; D005798:Genes, Bacterial; D008969:Molecular Sequence Data; D010957:Plasmids; D012045:Regulatory Sequences, Nucleic Acid
D001426:Bacterial Proteins; D004268:DNA-Binding Proteins