A single 43-bp sopC repeat of plasmid mini-F is sufficient to allow assembly of a functional nucleoprotein partition complex.

Abstract

Stable maintenance of the low-copy-number mini-F plasmid in Escherichia coil is dependent on a functional partition system. The sop partition region encodes proteins SopA and SopB and a cis-acting element sopC, which contains multiple sites to which SopB binds. We have found that SopB protein acting at sopC in vivo is associated with a marked effect on plasmid DNA supercolling, which may reflect the formation of a wrapped nucleoprotein complex. In this study, we demonstrate that a functional partition complex can form with a single 43-bp SopB binding site. Our experiments suggest that SopB bound at a single site nucleates the binding of additional SopB protein and wrapping of adjacent DNA sequences, such that approximately equal numbers of supercoils are restrained regardless of the number of tandem sopC repeats present. It is likely that this unusual nucleoprotein complex allows interaction of the plasmid with the partition apparatus.

P1 Partition Complex Assembly Involves Several Modes of Protein-DNA Recognition

“…The organization of the multiple copies of arm sites differs for integrative versus excisive recombination (in attP versus attL and attR, respectively), and the use of different arm sites and thus the architecture of Int-DNA complexes are modulated by binding of Xis to influence the directionality of the recombination reaction (27,28). The presence of multiple copies of recognition sequences for partition site-binding proteins is a general feature of many different partition systems, such as in the F plasmid sopC site, even though all copies may not be necessary for plasmid stability in the laboratory (29).…”

pTAR-Encoded Proteins in Plasmid Partitioning

“…The first gene encodes an ATPase with recognizable motifs (4,25,33). The second gene encodes a protein that can bind tightly to plasmid-specific iterated sequences within the cognate centromere analog (3,5,11,12,32,39). Homologs of plasmid partition genes with apparently analogous function have been reported in Bacillus (17,21,26,37) and in Caulobacter (31) spp., as well as in members of an increasing number of bacterial genera.…”

Distribution of Centromere-LikeparSSites in Bacteria: Insights from Comparative Genomics

“…In P1, as in F, parS is found downstream of parB, but this site consists of a single ϳ80-bp sequence that includes two ParB binding sites flanking a binding site for integration host factor (17,25). The binding of ParB and other partition factors to parS sites likely induces functionally significant topological changes in these DNA sequences (6,25,26,58).…”

“…The sequences and structures of plasmidic parS sequences are highly variable and often complex. For example, in the F plasmid, parS (sopC) consists of 12 tandem repeats of a 43-bp sequence (6). In P1, as in F, parS is found downstream of parB, but this site consists of a single ϳ80-bp sequence that includes two ParB binding sites flanking a binding site for integration host factor (17,25).…”