Autoregulation of the stability operon of IncFII plasmid NR1

Tabuchi, Akira; Min, You-Nong; Womble, David D.; Rownd, Robert H.

doi:10.1128/jb.174.23.7629-7634.1992

Cited by 18 publications

(11 citation statements)

References 29 publications

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“…Our main contribution is the finding that the P1 centromere analog, parS, can play an important, possibly catalytic role in that regulation. The P1 par operon is one of several partition operons that are regulated by the concerted action of both the proteins that they encode (24,29,30,32,33,35,47,55). Regulation of the partition operon of F appears also to be affected by the F-specific centromere sopC acting to enhance SopA-mediated repression (59).…”

Section: Discussionmentioning

confidence: 99%

Effects of the P1 Plasmid Centromere on Expression of P1 Partition Genes

Hao

Yarmolinsky

2002

J Bacteriol

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The partition operon of P1 plasmid encodes two proteins, ParA and ParB, required for the faithful segregation of plasmid copies to daughter cells. The operon is followed by a centromere analog, parS, at which ParB binds. ParA, a weak ATPase, represses the par promoter most effectively in its ADP-bound form. ParB can recruit ParA to parS, stimulate its ATPase, and significantly stimulate the repression. We report here that parS also participates in the regulation of expression of the par genes. A single chromosomal parS was shown to augment repression of several copies of the par promoter by severalfold. The repression increase was sensitive to the levels of ParA and ParB and to their ratio. The increase may be attributable to a conformational change in ParA mediated by the parS-ParB complex, possibly acting catalytically. We also observed an in cis effect of parS which enhanced expression of parB, presumably due to a selective modulation of the mRNA level. Although ParB had been earlier found to spread into and silence genes flanking parS, silencing of the par operon by ParB spreading was not significant. Based upon analogies between partitioning and septum placement, we speculate that the regulatory switch controlled by the parS-ParB complex might be essential for partitioning itself.Like many plasmids and chromosomes present in low copy numbers, plasmid prophage P1 is rarely lost at cell division. Its remarkable segregational stability is achieved by the mediation of partition proteins encoded by an operon of two genes. They act in conjunction with a cis-acting cluster of sites, parS, referred to as the plasmid centromere. Like many prokaryotic operons, the partition operon of P1 is regulated in a cooperative fashion by the proteins it encodes. The first protein of the operon, ParA, acts as repressor; the second, ParB, acts as corepressor (18).ParA binds in vitro to a region of 80 to 150 bp centered on a 20-bp imperfect palindrome overlapping the promoter, P par (9,11,29) (Fig.

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Section: Discussionmentioning

confidence: 99%

Effects of the P1 Plasmid Centromere on Expression of P1 Partition Genes

Hao

Yarmolinsky

2002

J Bacteriol

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“…A possible alternative mechanism for the observed stabilization provided by the parCBA operon is active partitioning. A partition system has been proposed for several plasmids, including plasmids F (20,35,36), R1/NR1 (23,49,50), and P1 (1). In general, most of the partition systems studied to date are contained on a single operon with a cis-acting site which acts as an incompatibility determinant and two genes encoding partition proteins capable of functioning either in cis or in trans.…”

Section: Discussionmentioning

confidence: 99%

Characterization of the stable maintenance properties of the par region of broad-host-range plasmid RK2

et al. 1996

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A 3.2-kb fragment encoding five genes, parCBA/DE, in two divergently transcribed operons promotes stable maintenance of the replicon of the broad-host-range plasmid RK2 in a vector-independent manner in Escherichia coli. The parDE operon has been shown to contribute to stabilization through the postsegregational killing of plasmid-free daughter cells, while the parCBA operon encodes a resolvase, ParA, that mediates the resolution of plasmid multimers through site-specific recombination. To date, evidence indicates that multimer resolution alone does not play a significant role in RK2 stable maintenance by the parCBA operon in E. coli. It has been proposed, instead, that the parCBA region encodes an additional stability mechanism, a partition system, that ensures that each daughter cell receives a plasmid copy at cell division. However, studies carried out to date have not directly determined the plasmid stabilization activity of the parCBA operon alone. An assessment was made of the relative contributions of postsegregational killing (parDE) and the putative partitioning system (parCBA) to the stabilization of mini-RK2 replicons in E. coli. Mini-RK2 replicons carrying either the entire 3.2-kb (parCBA/DE) fragment or the 2.3-kb parCBA region alone were found to be stably maintained in two E. coli strains tested. The stabilization found is not due to resolution of multimers. The stabilizing effectiveness of parCBA was substantially reduced when the plasmid copy number was lowered, as in the case of E. coli cells carrying a temperature-sensitive mini-RK2 replicon grown at a nonpermissive temperature. The presence of the entire 3.2-kb region effectively stabilized the replicon, however, under both low-and high-copy-number conditions. In those instances of decreased plasmid copy number, the postsegregational killing activity, encoded by parDE, either as part of the 3.2-kb fragment or alone played the major role in the stabilization of mini-RK2 replicons within the growing bacterial population. Our findings indicate that the parCBA operon functions to stabilize by a mechanism other than cell killing and resolution of plasmid multimers, while the parDE operon functions solely to stabilize plasmids by cell killing. The relative contribution of each system to stabilization depends on plasmid copy number and the particular E. coli host.

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“…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.…”

mentioning

confidence: 99%

“…The most thoroughly studied par operons, those of plasmids P1, F, R1, and NR1, are simple in structure and exhibit a number of similarities. Each consists of an autogenously regulated gene pair (10,19,22,32,39) and a centromere analog that is either upstream (for R1 [7] and NR1 [38]) or downstream (for P1 [1] and F [34]). The first gene encodes an ATPase with recognizable motifs (4,25,33).…”

mentioning

confidence: 99%