51
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Schaechter M. Escherichia coli and Salmonella 2000: the View From Here. EcoSal Plus 2004; 1. [PMID: 26443369 DOI: 10.1128/ecosalplus.1.4] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2004] [Indexed: 06/05/2023]
Abstract
In 1995, an editorial in Science (267:1575) commented that predictions made some 25 years previously regarding "Biology and the Future of Man" were largely fulfilled but that "the most revolutionary and unexpected findings were not predicted." We would be glad to do as well! As we stated at the beginning, our work as editors of the Escherichia coli and Salmonella book did not endow us with special powers of prophecy but it does permit us to express our excitement for the future. In our opinion, E. coli and S. enterica will continue to play a central role in biological research. This is not because they are intrinsically more interesting than any other bacteria, as we believe that all bacteria are equally interesting. However, knowledge builds on knowledge, and it is here that these two species continue to have a large edge not only over other microorganisms but also, for some time to come, over all other forms of life. It is interesting in this connection that biotechnology, having made detours through other microorganisms, always seems to return to E. coli.
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52
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González-Huici V, Alcorlo M, Salas M, Hermoso JM. Phage phi29 proteins p1 and p17 are required for efficient binding of architectural protein p6 to viral DNA in vivo. J Bacteriol 2004; 186:8401-6. [PMID: 15576790 PMCID: PMC532405 DOI: 10.1128/jb.186.24.8401-8406.2004] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2004] [Accepted: 09/01/2004] [Indexed: 11/20/2022] Open
Abstract
Bacteriophage phi29 protein p6 is a viral architectural protein, which binds along the whole linear phi29 DNA in vivo and is involved in initiation of DNA replication and transcription control. Protein p1 is a membrane-associated viral protein, proposed to attach the viral genome to the cell membrane. Protein p17 is involved in pulling phi29 DNA into the cell during the injection process. We have used chromatin immunoprecipitation and real-time PCR to analyze in vivo p6 binding to DNA in cells infected with phi29 sus1 or sus17 mutants; in both cases p6 binding is significantly decreased all along phi29 DNA. phi29 DNA is topologically constrained in vivo, and p6 binding is highly increased in the presence of novobiocin, a gyrase inhibitor that produces a loss of DNA negative superhelicity. Here we show that, in cells infected with phi29 sus1 or sus17 mutants, the increase of p6 binding by novobiocin is even higher than in cells containing p1 and p17, alleviating the p6 binding deficiency. Therefore, proteins p1 and p17 could be required to restrain the proper topology of phi29 DNA, which would explain the impaired DNA replication observed in cells infected with sus1 or sus17 mutants.
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Affiliation(s)
- Víctor González-Huici
- Instituto de Biología Molecular Eladio Viñuela (CSIC), Centro de Biología Molecular Severo Ochoa (CSIC-UAM), Universidad Autónoma, Canto Blanco, 28049 Madrid, Spain
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53
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Hoischen C, Bolshoy A, Gerdes K, Diekmann S. Centromere parC of plasmid R1 is curved. Nucleic Acids Res 2004; 32:5907-15. [PMID: 15528638 PMCID: PMC528805 DOI: 10.1093/nar/gkh920] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
The centromere sequence parC of Escherichia coli low-copy-number plasmid R1 consists of two sets of 11 bp iterated sequences. Here we analysed the intrinsic sequence-directed curvature of parC by its migration anomaly in polyacrylamide gels. The 159 bp long parC is strongly curved with anomaly values (k-factors) close to 2. The properties of the parC curvature agree with those of other curved DNA sequences. parC contains two regions of 5-fold repeated iterons separated by 39 bp. We modified 4 bp within this intermediate sequence so that we could analyse the two 5-fold repeated regions independently. The analysis shows that the two repeat regions are not independently curved parts of parC but that the overall curvature is a property of the whole fragment. Since the centromere sequence of an E.coli plasmid as well as eukaryotic centromere sequences show DNA curvature, we speculate that curvature might be a general property of centromeres.
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Affiliation(s)
- Christian Hoischen
- Institute for Molecular Biotechnology e.V., Beutenbergstr. 11, D-07745 Jena, Germany
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54
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Wang JD, Rokop ME, Barker MM, Hanson NR, Grossman AD. Multicopy plasmids affect replisome positioning in Bacillus subtilis. J Bacteriol 2004; 186:7084-90. [PMID: 15489419 PMCID: PMC523195 DOI: 10.1128/jb.186.21.7084-7090.2004] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2004] [Accepted: 08/09/2004] [Indexed: 11/20/2022] Open
Abstract
The DNA replication machinery, various regions of the chromosome, and some plasmids occupy characteristic subcellular positions in bacterial cells. We visualized the location of a multicopy plasmid, pHP13, in living cells of Bacillus subtilis using an array of lac operators and LacI-green fluorescent protein (GFP). In the majority of cells, plasmids appeared to be highly mobile and randomly distributed. In a small fraction of cells, there appeared to be clusters of plasmids located predominantly at or near a cell pole. We also monitored the effects of the presence of multicopy plasmids on the position of DNA polymerase using a fusion of a subunit of DNA polymerase to GFP. Many of the plasmid-containing cells had extra foci of the replisome, and these were often found at uncharacteristic locations in the cell. Some of the replisome foci were dynamic and highly mobile, similar to what was observed for the plasmid. In contrast, replisome foci in plasmid-free cells were relatively stationary. Our results indicate that in B. subtilis, plasmid-associated replisomes are recruited to the subcellular position of the plasmid. Extending this notion to the chromosome, we postulated that the subcellular position of the chromosomally associated replisome is established by the subcellular location of oriC at the time of initiation of replication.
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Affiliation(s)
- Jue D Wang
- Department of Biology, Building 68-530, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
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55
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Abstract
Bacterial plasmids of low copy number, P1 prophage among them, are actively partitioned to nascent daughter cells. The process is typically mediated by a pair of plasmid-encoded proteins and a cis-acting DNA site or cluster of sites, referred to as the plasmid centromere. P1 ParB protein, which binds to the P1 centromere (parS), can spread for several kilobases along flanking DNA. We argue that studies of mutant ParB that demonstrated a strong correlation between spreading capacity and the ability to engage in partitioning may be misleading, and describe here a critical test of the dependence of partitioning on the spreading of the wild-type protein. Physical constraints imposed on the spreading of P1 ParB were found to have only a minor, but reproducible, effect on partitioning. We conclude that, whereas extensive ParB spreading is not required for partitioning, spreading may have an auxiliary role in the process.
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Affiliation(s)
- Oleg Rodionov
- Laboratory of Biochemistry, National Cancer Institute, NIH, Bldg 37, Room 6044C, 37 Convent Drive, Bethesda, MD 20892-4255, USA
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56
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Garcia-Russell N, Harmon TG, Le TQ, Amaladas NH, Mathewson RD, Segall AM. Unequal access of chromosomal regions to each other in Salmonella: probing chromosome structure with phage lambda integrase-mediated long-range rearrangements. Mol Microbiol 2004; 52:329-44. [PMID: 15066024 DOI: 10.1111/j.1365-2958.2004.03976.x] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
We have investigated the fluidity of the Salmonella chromosome architecture using the phage lambda site-specific recombination system as a probe. We determined how chromosome position affects the extent of integrase-mediated recombination between pairs of inversely oriented att sites at various loci. We also investigated the accessibility of each chromosomal att site to an extrachromosomal partner carried on a low-copy plasmid. Recombination events were assayed by semi-quantitative polymerase chain reaction of the attP product. The extent of recombination between the chromosome and the plasmid was generally higher than intrachromosomal recombination except for two loci, araA::attL and galT::attL, which gave no detectable recombination with any other locus. Based on 20 intervals, we found that chromosomal locations are not equally accessible to each other. Although multiple factors probably affect accessibility, the most important is the specific combination of the end-points used. Neither the size of the intervals nor the accessibility of individual end-points to extrachromosomal sequences is as important. These results suggest that the chromosome is not completely fluid but rather organized in some way, with barriers that limit the movement of DNA within the cell. The nature of the barriers involved in chromosomal organization remains to be determined.
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Affiliation(s)
- Nathalie Garcia-Russell
- Department of Biology and Center for Microbial Sciences, San Diego State University, 5500 Campanile Dr. LS416, San Diego, CA 92182-4614, USA
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57
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Hägg P, de Pohl JW, Abdulkarim F, Isaksson LA. A host/plasmid system that is not dependent on antibiotics and antibiotic resistance genes for stable plasmid maintenance in Escherichia coli. J Biotechnol 2004; 111:17-30. [PMID: 15196766 DOI: 10.1016/j.jbiotec.2004.03.010] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2003] [Revised: 03/16/2004] [Accepted: 03/19/2004] [Indexed: 11/29/2022]
Abstract
Uneven distribution of plasmid-based expression vectors to daughter cells during bacterial cell division results in an increasing proportion of plasmid free cells during growth. This is a major industrial problem leading to reduction of product yields and increased production costs during large-scale cultivation of vector-carrying bacteria. For this reason, a selection must be provided that kills the plasmid free cells. The most conventional method to obtain this desired selection is to insert some gene for antibiotic resistance in the plasmid and then grow the bacteria in the presence of the corresponding antibiotic. We describe here a host/plasmid Escherichia coli system with a totally stable plasmid that can be maintained without the use of antibiotic selection. The plasmid is maintained, since it carries the small essential gene infA (coding for translation initiation factor 1, IF1) in an E. coli strain that has been deleted for its chromosomal infA gene. As a result only plasmid carrying cells can grow, making the strain totally dependent on the maintenance of the plasmid. A selection based on antibiotics is thus not necessary during cultivation, and no antibiotic-resistance genes are present neither in the final strain nor in the final plasmid. Plasmid-free cells do not accumulate even after an extended period of continuous growth. Growth rates of the control and the plasmid harboring strains are indistinguishable from each other in both LB and defined media. The indicated approach can be used to modify existing production strains and plasmids to the described concept. The infA based plasmid stability system should eliminate industrial cultivation problems caused by the loss of expression vector and use of antibiotics in the cultivation medium. Also environmental problems caused by release of antibiotics and antibiotic resistance genes, that potentially can give horizontal gene transfer between bacterial populations, are eliminated.
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Affiliation(s)
- Peter Hägg
- Department of Microbiology, Svante Arrhenius väg 16F, Stockholm University, S-106 91 Stockholm, Sweden
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58
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Leonard TA, Butler PJG, Löwe J. Structural analysis of the chromosome segregation protein Spo0J from Thermus thermophilus. Mol Microbiol 2004; 53:419-32. [PMID: 15228524 DOI: 10.1111/j.1365-2958.2004.04133.x] [Citation(s) in RCA: 86] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Prokaryotic chromosomes and plasmids encode partitioning systems that are required for DNA segregation at cell division. The plasmid partitioning loci encode two proteins, ParA and ParB, and a cis-acting centromere-like site denoted parS. The chromosomally encoded homologues of ParA and ParB, Soj and Spo0J, play an active role in chromosome segregation during bacterial cell division and sporulation. Spo0J is a DNA-binding protein that binds to parS sites in vivo. We have solved the X-ray crystal structure of a C-terminally truncated Spo0J (amino acids 1-222) from Thermus thermophilus to 2.3 A resolution by multiwavelength anomalous dispersion. It is a DNA-binding protein with structural similarity to the helix-turn-helix (HTH) motif of the lambda repressor DNA-binding domain. The crystal structure is an antiparallel dimer with the recognition alpha-helices of the HTH motifs of each monomer separated by a distance of 34 A corresponding to the length of the helical repeat of B-DNA. Sedimentation velocity and equilibrium ultracentrifugation studies show that full-length Spo0J exists in a monomer-dimer equilibrium in solution and that Spo0J1-222 is exclusively monomeric. Sedimentation of the C-terminal domain of Spo0J shows it to be exclusively dimeric, confirming that the C-terminus is the primary dimerization domain. We hypothesize that the C-terminus mediates dimerization of Spo0J, thereby effectively increasing the local concentration of the N-termini, which most probably dimerize, as shown by our structure, upon binding to a cognate parS site.
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Affiliation(s)
- Thomas A Leonard
- MRC Laboratory of Molecular Biology, Hills Road, Cambridge CB2 2QH, UK.
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59
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Viollier PH, Thanbichler M, McGrath PT, West L, Meewan M, McAdams HH, Shapiro L. Rapid and sequential movement of individual chromosomal loci to specific subcellular locations during bacterial DNA replication. Proc Natl Acad Sci U S A 2004; 101:9257-62. [PMID: 15178755 PMCID: PMC438963 DOI: 10.1073/pnas.0402606101] [Citation(s) in RCA: 318] [Impact Index Per Article: 15.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The chromosomal origin and terminus of replication are precisely localized in bacterial cells. We examined the cellular position of 112 individual loci that are dispersed over the circular Caulobacter crescentus chromosome and found that in living cells each locus has a specific subcellular address and that these loci are arrayed in linear order along the long axis of the cell. Time-lapse microscopy of the location of the chromosomal origin and 10 selected loci in the origin-proximal half of the chromosome showed that during DNA replication, as the replisome sequentially copies each locus, the newly replicated DNA segments are moved in chronological order to their final subcellular destination in the nascent half of the predivisional cell. Thus, the remarkable organization of the chromosome is being established while DNA replication is still in progress. The fact that the movement of these 10 loci is, like that of the origin, directed and rapid, and occurs at a similar rate, suggests that the same molecular machinery serves to partition and place many, if not most, chromosomal loci at defined subcellular sites.
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Affiliation(s)
- Patrick H Viollier
- Department of Developmental Biology, Beckman Center, Stanford University School of Medicine, Stanford, CA 94305, USA
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60
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Boucher N, McNicoll F, Laverdière M, Rochette A, Chou MN, Papadopoulou B. The ribosomal RNA gene promoter and adjacent cis-acting DNA sequences govern plasmid DNA partitioning and stable inheritance in the parasitic protozoan Leishmania. Nucleic Acids Res 2004; 32:2925-36. [PMID: 15161957 PMCID: PMC419617 DOI: 10.1093/nar/gkh617] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Detailed analysis of the Leishmania donovani ribosomal RNA (rRNA) gene promoter region has allowed the identification of cis-acting sequences involved in plasmid DNA partitioning and stable plasmid inheritance. We report that plasmids bearing the 350 bp rRNA promoter along with the 200 bp region immediately 3' to the promoter exhibited a 6.5-fold increase in transformation frequency and were transmitted to daughter cells as single-copy molecules. This is in contrast to what has been observed for plasmid molecules in this organism so far. Moreover, we show that these low-copy-number plasmids displayed a remarkable mitotic stability in the absence of selective pressure. The region in the vicinity of the RNA pol I transcription initiation site, and also in the adjacent 200 nt, displays a complex structural organization and shares sequence similarity to the yeast autonomously replicating consensus sequence and centromere DNA elements. Deletion analyses indicated that these elements were necessary but not sufficient for plasmid DNA partitioning and stable inheritance, and that the rRNA promoter region was required for optimal function. These results suggest an interplay between RNA pol I transcription, DNA replication, DNA partitioning and mitotic stability in trypanosomatids. This is the first example of defined DNA elements for plasmid partitioning and stable inheritance in the protozoan parasite Leishmania.
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Affiliation(s)
- Nathalie Boucher
- Infectious Disease Research Center, CHUL Research Center, Faculty of Medicine, Laval University, Quebec, Canada
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61
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Jayaram M, Mehta S, Uzri D, Velmurugan S. Segregation of the yeast plasmid: similarities and contrasts with bacterial plasmid partitioning. Plasmid 2004; 51:162-78. [PMID: 15109823 DOI: 10.1016/j.plasmid.2004.02.005] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2004] [Revised: 02/23/2004] [Indexed: 11/18/2022]
Abstract
The high copy yeast plasmid 2 microm circle, like the well-studied low copy bacterial plasmids, utilizes two partitioning proteins and a cis-acting 'centromere'-like sequence for its stable propagation. Functionally, though, the protein and DNA constituents of the two partitioning systems are quite distinct. Key events in the yeast and bacterial segregation pathways are plasmid organization, localization, replication, 'counting' of replicated molecules and their distribution to daughter cells. We suggest that the two systems facilitate these common logistical steps by adapting to the physical, biochemical, and mechanical contexts in which the host chromosomes segregate.
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Affiliation(s)
- Makkuni Jayaram
- Section of Molecular Genetics and Microbiology, University of Texas at Austin, Austin, TX 78712, USA.
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62
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Abstract
In bacteria, chromosome segregation and DNA replication occur concurrently and there is no clear equivalent of a eukaryote mitotic spindle. Chromosome segregation can be viewed as a two-step process. As the first step, the origin of replication regions are segregated actively, probably by a mechanism involving an as yet unidentified motor protein or proteins, and held in position. The second step is the separation and migration of the rest of the chromosome probably driven by forces generated from various cellular processes such as DNA replication, transcription and transertion.
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Affiliation(s)
- Ling Juan Wu
- Sir William Dunn School of Pathology, University of Oxford, South Parks Road, Oxford OX1 3RE, UK.
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63
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Abstract
It is now clear that bacterial chromosomes rapidly separate in a manner independent of cell elongation, suggesting the existence of a mitotic apparatus in bacteria. Recent studies of bacterial cells reveal filamentous structures similar to the eukaryotic cytoskeleton, proteins that mediate polar chromosome anchoring during Bacillus subtilis sporulation, and SMC interacting proteins that are involved in chromosome condensation. A picture is thereby developing of how bacterial chromosomes are organized within the cell, how they are separated following duplication, and how these processes are coordinated with the cell cycle.
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Affiliation(s)
- Kit Pogliano
- Division of Biological Sciences, 9500 Gilman Drive, University of California-San Diego, La Jolla, CA 92093-0349, USA.
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64
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Abstract
Low copy-number bacterial replicons occupy specific locations in their host cells. Production of a GFP-Lac repressor hybrid protein in cells carrying F or P1 plasmids tagged with a lac operator array reveals that in smaller (younger) cells these plasmids are seen mainly as a single fluorescent focus at mid-cell, whereas larger cells tend to have two foci, one at each quarter-cell position. Duplication of the central focus is presumed to represent active partition of plasmid copies. We report here our investigation by time-lapse microscopy of the subsequent movement of these copies to the quarter positions. Following duplication of the central focus, the new foci migrated rapidly and directly to their quarter-cell destinations, where they remained until the next cell cycle. The speed of movement was about five times faster than poleward migration of oriC and 50 times faster than cell elongation. Aberrant positioning of mini-F lacking its sopC centromere demonstrated the requirement for the partition system in this localization process. From the measured number of F plasmid copies per cell it appears that each migrating focus contains two or more plasmid molecules. The molecular basis of this clustering, and evidence for phasing of the partition event in the cell cycle, are discussed.
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Affiliation(s)
- Scott Gordon
- Department of Molecular Biology and Microbiology, Tufts University Health Sciences Campus, Boston, Massachusetts, USA
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65
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Jacobs-Wagner C. Regulatory proteins with a sense of direction: cell cycle signalling network in Caulobacter. Mol Microbiol 2004; 51:7-13. [PMID: 14651607 DOI: 10.1046/j.1365-2958.2003.03828.x] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Localization of kinases and other signalling molecules at discrete cellular locations is often an essential component of signal transduction in eukaryotes. Caulobacter crescentus is a small, single-celled bacterium that presumably lacks intracellular organelles. Yet in Caulobacter, the subcellular distribution of several two-component signal transduction proteins involved in the control of polar morphogenesis and cell cycle progression changes from a fairly dispersed distribution to a tight accumulation at one or both poles in a spatial and temporal pattern that is reproduced during each cell cycle. This cell cycle-dependent choreography suggests that similarly to what happens in eukaryotes, protein localization provides a means of modulating signal transduction in bacteria. Recent studies have provided important insights into the biological role and the mechanisms for the differential localization of these bacterial signalling proteins during the Caulobacter cell cycle.
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Affiliation(s)
- Christine Jacobs-Wagner
- Department of Molecular, Cellular, and Developmental Biology, Yale University, New Haven, Connecticut 06520, USA.
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66
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Ouverney CC, Armitage GC, Relman DA. Single-cell enumeration of an uncultivated TM7 subgroup in the human subgingival crevice. Appl Environ Microbiol 2004; 69:6294-8. [PMID: 14532094 PMCID: PMC201210 DOI: 10.1128/aem.69.10.6294-6298.2003] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Specific oligonucleotide hybridization conditions were established for single-cell enumeration of uncultivated TM7 and IO25 bacteria by using clones expressing heterologous 16S rRNA. In situ analysis of human subgingival crevice specimens revealed that a greater proportion of samples from sites of chronic periodontitis than from healthy sites contained TM7 subgroup IO25. In addition, IO25 bacterial cells from periodontitis site samples were more abundant and fourfold longer than IO25 cells from healthy site samples.
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Affiliation(s)
- Cleber C Ouverney
- Department of Microbiology and Immunology, Stanford University, Stanford, California 94305, USA.
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67
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Møller-Jensen J, Borch J, Dam M, Jensen RB, Roepstorff P, Gerdes K. Bacterial mitosis: ParM of plasmid R1 moves plasmid DNA by an actin-like insertional polymerization mechanism. Mol Cell 2004; 12:1477-87. [PMID: 14690601 DOI: 10.1016/s1097-2765(03)00451-9] [Citation(s) in RCA: 172] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Bacterial DNA segregation takes place in an active and ordered fashion. In the case of Escherichia coli plasmid R1, the partitioning system (par) separates paired plasmid copies and moves them to opposite cell poles. Here we address the mechanism by which the three components of the R1 par system act together to generate the force required for plasmid movement during segregation. ParR protein binds cooperatively to the centromeric parC DNA region, thereby forming a complex that interacts with the filament-forming actin-like ParM protein in an ATP-dependent manner, suggesting that plasmid movement is powered by insertional polymerization of ParM. Consistently, we find that segregating plasmids are positioned at the ends of extending ParM filaments. Thus, the process of R1 plasmid segregation in E. coli appears to be mechanistically analogous to the actin-based motility operating in eukaryotic cells. In addition, we find evidence suggesting that plasmid pairing is required for ParM polymerization.
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Affiliation(s)
- Jakob Møller-Jensen
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark
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68
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Yamaichi Y, Niki H. migS, a cis-acting site that affects bipolar positioning of oriC on the Escherichia coli chromosome. EMBO J 2003; 23:221-33. [PMID: 14685268 PMCID: PMC1271666 DOI: 10.1038/sj.emboj.7600028] [Citation(s) in RCA: 85] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2003] [Accepted: 11/14/2003] [Indexed: 11/09/2022] Open
Abstract
During replication of the Escherichia coli chromosome, the replicated Ori domains migrate towards opposite cell poles, suggesting that a cis-acting site for bipolar migration is located in this region. To identify this cis-acting site, a series of mutants was constructed by splitting subchromosomes from the original chromosome. One mutant, containing a 720 kb subchromosome, was found to be defective in the bipolar positioning of oriC. The creation of deletion mutants allowed the identification of migS, a 25 bp sequence, as the cis-acting site for the bipolar positioning of oriC. When migS was located at the replication terminus, the chromosomal segment showed bipolar positioning. migS was able to rescue bipolar migration of plasmid DNA containing a mutation in the SopABC partitioning system. Interestingly, multiple copies of the migS sequence on a plasmid in trans inhibited the bipolar positioning of oriC. Taken together, these findings indicate that migS plays a crucial role in the bipolar positioning of oriC. In addition, real-time analysis of the dynamic morphological changes of nucleoids in wild-type and migS mutants suggests that bipolar positioning of the replicated oriC contributes to nucleoid organization.
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Affiliation(s)
- Yoshiharu Yamaichi
- Radioisotope Center, National Institute of Genetics, Yata 1111, Mishima 411-8540 Japan
- Graduate School of Medicine, Kumamoto University, Kuhonji 4-24-1, Kumamoto 862-0976, Japan
| | - Hironori Niki
- Radioisotope Center, National Institute of Genetics, Yata 1111, Mishima 411-8540 Japan
- National Institute of Genetics, Radioisotope Center, Yata 1111, Mishima 411-8540, Japan. Tel.: +81 55 981 6870; Fax: +81 55 981 6880/6871; E-mail:
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69
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Kruse T, Møller-Jensen J, Løbner-Olesen A, Gerdes K. Dysfunctional MreB inhibits chromosome segregation in Escherichia coli. EMBO J 2003; 22:5283-92. [PMID: 14517265 PMCID: PMC204487 DOI: 10.1093/emboj/cdg504] [Citation(s) in RCA: 237] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The mechanism of prokaryotic chromosome segregation is not known. MreB, an actin homolog, is a shape-determining factor in rod-shaped prokaryotic cells. Using immunofluorescence microscopy we found that MreB of Escherichia coli formed helical filaments located beneath the cell surface. Flow cytometric and cytological analyses indicated that MreB-depleted cells segregated their chromosomes in pairs, consistent with chromosome cohesion. Overexpression of wild-type MreB inhibited cell division but did not perturb chromosome segregation. Overexpression of mutant forms of MreB inhibited cell division, caused abnormal MreB filament morphology and induced severe localization defects of the nucleoid and of the oriC and terC chromosomal regions. The chromosomal terminus regions appeared cohered in both MreB-depleted cells and in cells overexpressing mutant forms of MreB. Our observations indicate that MreB filaments participate in directional chromosome movement and segregation.
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Affiliation(s)
- Thomas Kruse
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Odense, DK-5230 Odense M, Denmark
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70
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Nordström K, Gerdes K. Clustering versus random segregation of plasmids lacking a partitioning function: a plasmid paradox? Plasmid 2003; 50:95-101. [PMID: 12932735 DOI: 10.1016/s0147-619x(03)00056-8] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Plasmids lacking a functional partition system are randomly distributed to the daughter cells; plasmid-free daughter cells are formed with a frequency of (1/2)2n per cell and cell generation where 2n is the (average) copy number at cell division. Hence, the unit of segregation is one plasmid copy. However, plasmids form clusters in the cells. A putative solution to this potential paradox is presented: one plasmid copy at a time is recruited from the plasmid clusters to the replication factories that are located in the cell centres. Hence, replication offers the means of declustering that is necessary in a growing host population. The daughter copies diffuse freely and each copy may with equal probability end up in either of the two cell halves. In this way, the random segregation of the plasmids is coupled to replication and occurs continuously during the cell cycle, and is not linked to cell division. The unit of segregation is the plasmid copy and not the plasmid clusters. In contrast, the two daughters of a Par+ plasmid are directed in opposite directions by the plasmid-encoded partition system, thereby assuring that each daughter cell receives the plasmid.
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Affiliation(s)
- Kurt Nordström
- Department of Cell and Molecular Biology, Biomedical Center, Uppsala University, P.O. Box 596, Uppsala S-751 24, Sweden.
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71
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Wu LJ, Errington J. RacA and the Soj-Spo0J system combine to effect polar chromosome segregation in sporulating Bacillus subtilis. Mol Microbiol 2003; 49:1463-75. [PMID: 12950914 DOI: 10.1046/j.1365-2958.2003.03643.x] [Citation(s) in RCA: 166] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Sporulating cells of Bacillus subtilis undergo a highly polarized cell division and possess a specialized mechanism to move the oriC region of the chromosome close to the cell pole before septation. DivIVA protein, which localizes to the cell pole, and the Soj and Spo0J proteins, which associate with the chromosome, are part of the mechanism that delivers the chromosome to the cell pole. A sporulation-specific protein, RacA, encodes a third DNA-binding protein, which acts in conjunction with Soj and Spo0J to effect efficient polar chromosome segregation. divIVA mutants and soj racA double mutants have an unexpected phenotype in which specific markers to the left and right of oriC can be captured in the prespore compartment but the central oriC region is efficiently excluded. This 'residual' trapping requires Spo0J protein. We suggest that the Soj RacA DivIVA system is required to extract the oriC region from its position determined by the vegetative chromosome segregation machinery and anchor it to the cell pole.
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Affiliation(s)
- Ling Juan Wu
- Sir William Dunn School of Pathology, University of Oxford, South Parks Road, Oxford, OX1 3RE, UK
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72
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Alpert CA, Crutz-Le Coq AM, Malleret C, Zagorec M. Characterization of a theta-type plasmid from Lactobacillus sakei: a potential basis for low-copy-number vectors in lactobacilli. Appl Environ Microbiol 2003; 69:5574-84. [PMID: 12957947 PMCID: PMC194969 DOI: 10.1128/aem.69.9.5574-5584.2003] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2003] [Accepted: 06/16/2003] [Indexed: 11/20/2022] Open
Abstract
The complete nucleotide sequence of the 13-kb plasmid pRV500, isolated from Lactobacillus sakei RV332, was determined. Sequence analysis enabled the identification of genes coding for a putative type I restriction-modification system, two genes coding for putative recombinases of the integrase family, and a region likely involved in replication. The structural features of this region, comprising a putative ori segment containing 11- and 22-bp repeats and a repA gene coding for a putative initiator protein, indicated that pRV500 belongs to the pUCL287 subfamily of theta-type replicons. A 3.7-kb fragment encompassing this region was fused to an Escherichia coli replicon to produce the shuttle vector pRV566 and was observed to be functional in L. sakei for plasmid replication. The L. sakei replicon alone could not support replication in E. coli. Plasmid pRV500 and its derivative pRV566 were determined to be at very low copy numbers in L. sakei. pRV566 was maintained at a reasonable rate over 20 generations in several lactobacilli, such as Lactobacillus curvatus, Lactobacillus casei, and Lactobacillus plantarum, in addition to L. sakei, making it an interesting basis for developing vectors. Sequence relationships with other plasmids are described and discussed.
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Affiliation(s)
- Carl-Alfred Alpert
- Flore Lactique et Environnement Carné, Institut National de la Recherche Agronomique, 78350 Jouy en Josas, France
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73
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Barillà D, Hayes F. Architecture of the ParF*ParG protein complex involved in prokaryotic DNA segregation. Mol Microbiol 2003; 49:487-99. [PMID: 12828644 DOI: 10.1046/j.1365-2958.2003.03564.x] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The mechanism by which low copy number plasmids are segregated at cell division involves the concerted action of two plasmid-encoded proteins that assemble on a centromere-like site. This study explores the topology of the DNA segregation machinery specified by the parFG locus of TP228, a partition system which is phylogenetically distinct from more well-characterized archetypes. A variety of genetic, biochemical and biophysical strategies revealed that the ParG protein is dimeric. ParF, which is more closely related to the cell division regulator MinD than to the prototypical ParA partition protein of plasmid P1, is instead multimeric and its polymeric state appears to be modulated by ATP which correlates with the proposed ATP-binding activity of ParF. ParG interacts in a sequence-specific manner with the DNA region upstream of the parFG locus and this binding is modulated by ParF. Intriguingly, the ParF and ParG proteins form at least two types of discrete complex in the absence of this region suggesting that the assembly dynamics of these proteins onto DNA is intricate.
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Affiliation(s)
- Daniela Barillà
- Department of Biomolecular Sciences, University of Manchester Institute of Science and Technology, PO Box 88, Manchester M60 1QD, UK
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74
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Jensen RB, Shapiro L. Cell-cycle-regulated expression and subcellular localization of the Caulobacter crescentus SMC chromosome structural protein. J Bacteriol 2003; 185:3068-75. [PMID: 12730166 PMCID: PMC154060 DOI: 10.1128/jb.185.10.3068-3075.2003] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
Structural maintenance of chromosomes proteins (SMCs) bind to DNA and function to ensure proper chromosome organization in both eukaryotes and bacteria. Caulobacter crescentus possesses a single SMC homolog that plays a role in organizing and segregating daughter chromosomes. Approximately 1,500 to 2,000 SMC molecules are present per cell during active growth, corresponding to one SMC complex per 6,000 to 8,000 bp of chromosomal DNA. Although transcription from the smc promoter is induced during early S phase, a cell cycle transcription pattern previously observed with multiple DNA replication and repair genes, the SMC protein is present throughout the entire cell cycle. Examination of the intracellular location of SMC showed that in swarmer cells, which do not replicate DNA, the protein forms two or three foci. Stalked cells, which are actively engaged in DNA replication, have three or four SMC foci per cell. The SMC foci appear randomly distributed in the cell. Many predivisional cells have bright polar SMC foci, which are lost upon cell division. Thus, chromosome compaction likely involves dynamic aggregates of SMC bound to DNA. The aggregation pattern changes as a function of the cell cycle both during and upon completion of chromosome replication.
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Affiliation(s)
- Rasmus B Jensen
- Department of Developmental Biology, Beckman Center, Stanford University School of Medicine, Stanford, California 94305-5329, USA
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75
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Lawley TD, Taylor DE. Characterization of the double-partitioning modules of R27: correlating plasmid stability with plasmid localization. J Bacteriol 2003; 185:3060-7. [PMID: 12730165 PMCID: PMC154067 DOI: 10.1128/jb.185.10.3060-3067.2003] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Plasmid R27 contains two independent partitioning modules, designated Par1 and Par2, within transfer region 2. Par1 is member of the type I partitioning family (Walker-type ATPase), and Par2 is a member of the type II partitioning family (actin-type ATPase). Stability tests of cloned Par1 and Par2 and insertional disruptions of Par1 and Par2 within R27 demonstrated that Par1 is the major stability determinant whereas Par2 is the minor stability determinant. Creation of double-partitioning mutants resulted in R27 integrating into the chromosome, suggesting that at least one partitioning module is required for R27 to exist in the extrachromosomal form. Using the lacO/LacI-green fluorescent protein (GFP) system, we labeled and visualized R27 and R27 partitioning mutants (Par1(-) and Par2(-)) under different growth conditions in live Escherichia coli cells. Plasmid R27 was visualized as the discrete GFP foci present at the mid- and quarter-cell regions in >99% of the cells. Time lapse experiments demonstrated that an increase in R27 plasmid foci resulted from focus duplication in either the mid- or quarter-cell regions of E. coli. Both R27 Par(-) variants gave a high percentage of plasmidless cells, as suggested by a uniform GFP signal, and cells with GFP patterns scattered throughout the entire cell, suggesting that plasmid molecules are randomly distributed throughout the cytoplasm. Those cells that did contain R27 Par(-) with one or two discrete foci had localization patterns that were statistically different from those formed with wild-type R27. Therefore, these results suggest that partitioning-impaired plasmids are characterized by individual and clustered plasmids that are randomly located within the host cytoplasm.
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Affiliation(s)
- Trevor D Lawley
- Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada T6G 2R3
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76
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Simpson AE, Skurray RA, Firth N. A single gene on the staphylococcal multiresistance plasmid pSK1 encodes a novel partitioning system. J Bacteriol 2003; 185:2143-52. [PMID: 12644483 PMCID: PMC151481 DOI: 10.1128/jb.185.7.2143-2152.2003] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The orf245 gene is located immediately upstream of, and divergently transcribed from, the replication initiation gene, rep, of the Staphylococcus aureus multiresistance plasmid pSK1, and related genes have been found in association with a range of evolutionarily distinct replication genes on plasmids from various gram-positive genera. orf245 has been shown previously to extend the segregational stability of a pSK1 minireplicon. Here we describe an investigation into the basis of orf245-mediated stabilization. orf245 was not found to influence transcription of pSK1 rep, indicating that it is not directly involved in plasmid replication. This was confirmed by demonstrating that orf245 is able to enhance the segregational stability of heterologous theta- and rolling-circle-replicating replicons, suggesting that it encodes a plasmid maintenance function. Evidence inconsistent with postsegregational killing and multimer resolution mechanisms was obtained; however, the intergenic region upstream of orf245 was found to mediate orf245-dependent incompatibility, as would be expected if it encodes a cis-acting centromere-like site. Taken together, these findings implicate active partitioning as the probable basis of the activity of orf245, which is therefore redesignated par. Since it is unrelated to any gene known to play a role in plasmid segregation, it seems likely that pSK1 par potentially represents the prototype of a novel class of active partitioning systems that are distinguished by their capacity to enhance plasmid segregational stability via a single protein-encoding gene.
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Affiliation(s)
- Alice E Simpson
- School of Biological Sciences, University of Sydney, Sydney, New South Wales 2006, Australia
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77
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Grady R, Hayes F. Axe-Txe, a broad-spectrum proteic toxin-antitoxin system specified by a multidrug-resistant, clinical isolate of Enterococcus faecium. Mol Microbiol 2003; 47:1419-32. [PMID: 12603745 DOI: 10.1046/j.1365-2958.2003.03387.x] [Citation(s) in RCA: 177] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Enterococcal species of bacteria are now acknowledged as leading causes of bacteraemia and other serious nosocomial infections. However, surprisingly little is known about the molecular mechanisms that promote the segregational stability of antibiotic resistance and other plasmids in these bacteria. Plasmid pRUM (24 873 bp) is a multidrug resistance plasmid identified in a clinical isolate of Enterococcus faecium. A novel proteic-based toxin-antitoxin cassette identified on pRUM was demonstrated to be a functional segregational stability module in both its native host and evolutionarily diverse bacterial species. Induced expression of the toxin protein (Txe) of this system resulted in growth inhibition in Escherichia coli. The toxic effect of Txe was alleviated by co-expression of the antitoxin protein, Axe. Homologues of the axe and txe genes are present in the genomes of a diversity of Eubacteria. These homologues (yefM-yoeB) present in the E. coli chromosome function as a toxin-antitoxin mechanism, although the Axe and YefM antitoxin components demonstrate specificity for their cognate toxin proteins in vivo. Axe-Txe is one of the first functional proteic toxin-antitoxin systems to be accurately described for Gram-positive bacteria.
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Affiliation(s)
- Ruth Grady
- Department of Biomolecular Sciences, University of Manchester Institute of Science and Technology (UMIST), PO Box 88, Manchester M60 1QD, UK
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78
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Figge RM, Easter J, Gober JW. Productive interaction between the chromosome partitioning proteins, ParA and ParB, is required for the progression of the cell cycle in Caulobacter crescentus. Mol Microbiol 2003; 47:1225-37. [PMID: 12603730 DOI: 10.1046/j.1365-2958.2003.03367.x] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
In Caulobacter crescentus the partitioning proteins ParA and ParB operate a molecular switch that couples chromosome partitioning to cytokinesis. Homologues of these proteins have been shown to be important for the stable inheritance of F-plasmids and the prophage form of bacteriophage P1. In C. crescentus, ParB binds to sequences adjacent to the origin of replication and is required for the initiation of cell division. Additionally, ParB influences the nucleotide-bound state of ParA by acting as a nucleotide exchange factor. Here we have performed a genetic analysis of the chromosome partitioning protein ParB. We show that C. crescentus ParB, like its plasmid homologues, is composed of three domains: a carboxyl-terminal dimerization domain; a central DNA-binding, helix-turn-helix domain; and an amino-terminal domain required for the interaction with ParA. In vivo expression of amino-terminally deleted parB alleles has a dominant lethal effect resulting in the inhibition of cell division. Fluorescent in situ hybridization experiments indicate that this phenotype is not caused by a chromosome partitioning defect, but by the reversal of the amounts of ATP- versus ADP- bound ParA inside the cell. We present evidence suggesting that amino-terminally truncated and full-length, wild-type ParB form heterodimers which fail to interact with ParA, thereby reversing the intracellular ParA-ATP to ParA-ADP ratio. We hypothesize that the amino-terminus of ParB is required to regulate the nucleotide exchange of ParA which, in turn, regulates the initiation of cell division.
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Affiliation(s)
- Rainer M Figge
- Department of Chemistry and Biochemistry and the Molecular Biology Institute, University of California, Los Angeles, CA 90095-1569, USA
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79
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Affiliation(s)
- Jeffery Errington
- Sir William Dunn School of Pathology, University of Oxford, South Parks Road, Oxford OX1 3RE, UK.
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80
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Lee PS, Lin DCH, Moriya S, Grossman AD. Effects of the chromosome partitioning protein Spo0J (ParB) on oriC positioning and replication initiation in Bacillus subtilis. J Bacteriol 2003; 185:1326-37. [PMID: 12562803 PMCID: PMC142880 DOI: 10.1128/jb.185.4.1326-1337.2003] [Citation(s) in RCA: 88] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Spo0J (ParB) of Bacillus subtilis is a DNA-binding protein that belongs to a conserved family of proteins required for efficient plasmid and chromosome partitioning in many bacterial species. We found that Spo0J contributes to the positioning of the chromosomal oriC region, but probably not by recruiting the origin regions to specific subcellular locations. In wild-type cells during exponential growth, duplicated origin regions were generally positioned around the cell quarters. In a spo0J null mutant, sister origin regions were often closer together, nearer to midcell. We found, by using a Spo0J-green fluorescent protein [GFP] fusion, that the subcellular location of Spo0J was a consequence of the chromosomal positions of the Spo0J binding sites. When an array of binding sites (parS sites) were inserted at various chromosomal locations in the absence of six of the eight known parS sites, Spo0J-GFP was no longer found predominantly at the cell quarters, indicating that Spo0J is not sufficient to recruit chromosomal parS sites to the cell quarters. spo0J also affected chromosome positioning during sporulation. A spo0J null mutant showed an increase in the number of cells with some origin-distal regions located in the forespore. In addition, a spo0J null mutation caused an increase in the number of foci per cell of LacI-GFP bound to arrays of lac operators inserted in various positions in the chromosome, including the origin region, an increase in the DNA-protein ratio, and an increase in origins per cell, as determined by flow cytometry. These results indicate that the spo0J mutant produced a significant proportion of cells with increased chromosome content, probably due to increased and asynchronous initiation of DNA replication.
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Affiliation(s)
- Philina S Lee
- Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
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81
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Abstract
Eukaryotic chromosomes are anchored to a spindle apparatus during mitosis, but no such structure is known during chromosome segregation in bacteria. When sister chromosomes are segregated during sporulation in Bacillus subtilis, the replication origin regions migrate to opposite poles of the cell. If and how origin regions are fastened at the poles has not been determined. Here we describe a developmental protein, RacA, that acts as a bridge between the origin region and the cell poles. We propose that RacA assembles into an adhesive patch at a centromere-like element near the origin, causing chromosomes to stick at the poles.
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Affiliation(s)
- Sigal Ben-Yehuda
- Department of Molecular and Cellular Biology, Harvard University, 16 Divinity Avenue, Cambridge, MA 02138, USA
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82
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Abstract
Recent studies have made great strides toward our understanding of the mechanisms of microbial chromosome segregation and partitioning. This review first describes the mechanisms that function to segregate newly replicated chromosomes, generating daughter molecules that are viable substrates for partitioning. Then experiments that address the mechanisms of bulk chromosome movement are summarized. Recent evidence indicates that a stationary DNA replication factory may be responsible for supplying the force necessary to move newly duplicated DNA toward the cell poles. Some factors contributing to the directionality of chromosome movement probably include centromere-like-binding proteins, DNA condensation proteins, and DNA translocation proteins.
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Affiliation(s)
- Geoffrey C Draper
- Department of Chemistry and Biochemistry, University of California, Los Angeles, 90095-1569, USA
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83
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Surtees JA, Funnell BE. Plasmid and chromosome traffic control: how ParA and ParB drive partition. Curr Top Dev Biol 2003; 56:145-80. [PMID: 14584729 DOI: 10.1016/s0070-2153(03)01010-x] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Affiliation(s)
- Jennifer A Surtees
- Department of Medical Genetics and Microbiology, University of Toronto, Toronto, Ontario M5S 1A8, Canada
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84
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van den Ent F, Møller-Jensen J, Amos LA, Gerdes K, Löwe J. F-actin-like filaments formed by plasmid segregation protein ParM. EMBO J 2002; 21:6935-43. [PMID: 12486014 PMCID: PMC139093 DOI: 10.1093/emboj/cdf672] [Citation(s) in RCA: 217] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
It was the general belief that DNA partitioning in prokaryotes is independent of a cytoskeletal structure, which in eukaryotic cells is indispensable for DNA segregation. Recently, however, immunofluorescence microscopy revealed highly dynamic, filamentous structures along the longitudinal axis of Escherichia coli formed by ParM, a plasmid-encoded protein required for accurate segregation of low-copy-number plasmid R1. We show here that ParM polymerizes into double helical protofilaments with a longitudinal repeat similar to filamentous actin (F-actin) and MreB filaments that maintain the cell shape of non-spherical bacteria. The crystal structure of ParM with and without ADP demonstrates that it is a member of the actin family of proteins and shows a domain movement of 25 degrees upon nucleotide binding. Furthermore, the crystal structure of ParM reveals major differences in the protofilament interface compared with F-actin, despite the similar arrangement of the subunits within the filaments. Thus, there is now evidence for cytoskeletal structures, formed by actin-like filaments that are involved in plasmid partitioning in E.coli.
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Affiliation(s)
| | - Jakob Møller-Jensen
- MRC Laboratory of Molecular Biology, Hills Road, Cambridge CB2 2QH, UK and
Department of Biochemistry and Molecular Biology, University of Southern Denmark, DK-5230 Odense M, Denmark Corresponding author e-mail: F.van den Ent and J.Møller-Jensen contributed equally to this work
| | | | - Kenn Gerdes
- MRC Laboratory of Molecular Biology, Hills Road, Cambridge CB2 2QH, UK and
Department of Biochemistry and Molecular Biology, University of Southern Denmark, DK-5230 Odense M, Denmark Corresponding author e-mail: F.van den Ent and J.Møller-Jensen contributed equally to this work
| | - Jan Löwe
- MRC Laboratory of Molecular Biology, Hills Road, Cambridge CB2 2QH, UK and
Department of Biochemistry and Molecular Biology, University of Southern Denmark, DK-5230 Odense M, Denmark Corresponding author e-mail: F.van den Ent and J.Møller-Jensen contributed equally to this work
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85
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Abanes-De Mello A, Sun YL, Aung S, Pogliano K. A cytoskeleton-like role for the bacterial cell wall during engulfment of the Bacillus subtilis forespore. Genes Dev 2002; 16:3253-64. [PMID: 12502745 PMCID: PMC187501 DOI: 10.1101/gad.1039902] [Citation(s) in RCA: 100] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
A hallmark of bacterial endospore formation is engulfment, during which the membrane of one cell (the mother cell) migrates around the future spore, enclosing it in the mother cell cytoplasm. Bacteria lack proteins required for eukaryotic phagocytosis, and previously proteins required for membrane migration remained unidentified. Here we provide cell biological and genetic evidence that three membrane proteins synthesized in the mother cell are required for membrane migration as well as for earlier steps in engulfment. Biochemical studies demonstrate that one of these proteins, SpoIID, is a cell wall hydrolase, suggesting that membrane migration in bacteria can be driven by membrane-anchored cell wall hydrolases. We propose that the bacterial cell wall plays a role analogous to that of the actin and tubulin network of eukaryotic cells, providing a scaffold along which proteins can move.
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86
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Abstract
Bacteria are often highly polarized, exhibiting specialized structures at or near the ends of the cell. Among such structures are actin-organizing centers, which mediate the movement of certain pathogenic bacteria within the cytoplasm of an animal host cell; organized arrays of membrane receptors, which govern chemosensory behavior in swimming bacteria; and asymmetrically positioned septa, which generate specialized progeny in differentiating bacteria. This polarization is orchestrated by complex and dynamic changes in the subcellular localization of signal transduction and cytoskeleton proteins as well as of specific regions of the chromosome. Recent work has provided information on how dynamic subcellular localization occurs and how it is exploited by the bacterial cell. The main task of a bacterial cell is to survive and duplicate itself. The bacterium must replicate its genetic material and divide at the correct site in the cell and at the correct time in the cell cycle with high precision. Each kind of bacterium also executes its own strategy to find nutrients in its habitat and to cope with conditions of stress from its environment. This involves moving toward food, adapting to environmental extremes, and, in many cases, entering and exploiting a eukaryotic host. These activities often involve processes that take place at or near the poles of the cell. Here we explore some of the schemes bacteria use to orchestrate dynamic changes at their poles and how these polar events execute cellular functions. In spite of their small size, bacteria have a remarkably complex internal organization and external architecture. Bacterial cells are inherently asymmetric, some more obviously so than others. The most easily recognized asymmetries involve surface structures, e.g., flagella, pili, and stalks that are preferentially assembled at one pole by many bacteria. "New" poles generated at the cell division plane differ from old poles from the previous round of cell division. Even in Escherichia coli, which is generally thought to be symmetrical, old poles are more static than new poles with respect to cell wall assembly (1), and they differ in the deposition of phospholipid domains (2). There are many instances of differential polar functions; among these is the preferential use of old poles when attaching to host cells as in the interaction of Bradyrhizobium with plant root hairs (3) or the polar pili-mediated attachment of the Pseudomonas aeruginosa pathogen to tracheal epithelia (4). An unusual polar organelle that mediates directed motility on solid surfaces is found in the nonpathogenic bacterium Myxococcus xanthus. The gliding motility of this bacterium is propelled by a nozzle-like structure that squirts a polysaccharide-containing slime from the pole of the cell (5). Interestingly, M. xanthus, which has nozzles at both poles, can reverse direction by closing one nozzle and opening the other in response to end-to-end interactions between cells.
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Affiliation(s)
- Lucy Shapiro
- Department of Developmental Biology, Stanford University School of Medicine, B300 Beckman Center, Stanford, CA 94305, USA.
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87
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Abstract
Growth of the bacterial cell involves proteins that assemble into dynamic localized structures that are required for cellular morphogenesis and division. During the past year, the continued application of fluorescence microscopy has led to the discovery of novel actin-like filaments involved in cell shape and plasmid DNA segregation, and to new insights into the regulation and dynamics of the Z-ring. Studies on the Min proteins, which rapidly oscillate between the cell poles to spatially regulate Z-ring assembly, has led to a biochemical basis for the oscillation and a suggestion that MinD assembles into dynamic filaments. These studies further demonstrate that the eukaryotic cytoskeleton had its origins in bacteria.
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Affiliation(s)
- Joe Lutkenhaus
- Department of Microbiology, Molecular Genetics and Immunology, University of Kansas Medical Center, Kansas City, KS 66160, USA.
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88
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Abstract
Recent studies have shown that plasmids are organized inside bacterial cells in a remarkably complex way. Plasmids containing active partitioning systems are tethered to specific regions of the cell, and the number and position of plasmid molecules within the cell are coordinated with the bacterial host cell cycle and growth rate. Plasmids belonging to different incompatibility groups are also tethered to different sites within the cell, and segregate at different times relative to one another and to the bacterial cell cycle. Recent studies suggest that many of these observations regarding subcellular plasmid dynamics formulated for Escherichia coli plasmids may be broadly conserved.
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Affiliation(s)
- Joe Pogliano
- Division of Biology, University of California, San Diego, 4105 Bonner Hall, 9500 Gilman Drive, La Jolla, CA 92093-0349, USA.
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89
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Jakimowicz D, Chater K, Zakrzewska-Czerwínska J. The ParB protein of Streptomyces coelicolor A3(2) recognizes a cluster of parS sequences within the origin-proximal region of the linear chromosome. Mol Microbiol 2002; 45:1365-77. [PMID: 12207703 DOI: 10.1046/j.1365-2958.2002.03102.x] [Citation(s) in RCA: 76] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The mycelial prokaryote Streptomyces coelicolor A3(2) possesses a large linear chromosome (8.67 Mb) with a centrally located origin of replication (oriC). Recently, chromosome partitioning genes (parA and parB) and putative ParB binding sites (parS sequences) were identified in its genome. The S. coelicolor chromosome contains more parS sequences than any other bacterial chromosome characterized so far. Twenty of the 24 parS sequences are densely packed within a relatively short distance (approximately 200 kb) around oriC. A series of in vitro and in vivo experiments showed that S. coelicolor ParB protein interacts specifically with the parS sequences, albeit with a rather low affinity. Our results suggested that the binding of ParB is not only determined by the parS sequence, but also by the location of target DNA close to oriC. The unusually high number and close proximity to each other of the parS sites, together with in vivo and in vitro evidence that multiple ParB molecules may assemble along the DNA from an initial ParB-parS complex, suggest that a large DNA segment around the replication origin may form a massive nucleoprotein complex as part of the replication-partitioning cycle.
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90
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Easter J, Gober JW. ParB-stimulated nucleotide exchange regulates a switch in functionally distinct ParA activities. Mol Cell 2002; 10:427-34. [PMID: 12191487 DOI: 10.1016/s1097-2765(02)00594-4] [Citation(s) in RCA: 84] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
ParA and ParB of Caulobacter crescentus belong to a conserved family of bacterial proteins implicated in chromosome segregation. ParB binds to DNA sequences adjacent to the origin of replication and localizes to opposite cell poles shortly following the initiation of DNA replication. ParA has homology to a conserved and widespread family of ATPases. Here, we show that ParB regulates the ParA ATPase activity by promoting nucleotide exchange in a fashion reminiscent of the exchange factors of eukaryotic G proteins. Furthermore, we demonstrate that ADP-bound ParA binds single-stranded DNA, whereas the ATP-bound form dissociates ParB from its DNA binding sites. Increasing the fraction of ParA-ADP in the cell inhibits cell division, suggesting that this simple nucleotide switch may regulate cytokinesis.
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Affiliation(s)
- Jesse Easter
- Department of Chemistry and Biochemistry and the Molecular Biology Institute, University of California, Los Angeles 90095, USA
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91
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Wu LJ, Errington J. A large dispersed chromosomal region required for chromosome segregation in sporulating cells of Bacillus subtilis. EMBO J 2002; 21:4001-11. [PMID: 12145201 PMCID: PMC126140 DOI: 10.1093/emboj/cdf393] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The cis-acting sequences required for chromosome segregation are poorly understood in most organisms, including bacteria. Sporulating cells of Bacillus subtilis undergo an unusual asymmetric cell division during which the origin of DNA replication (oriC) region of the chromosome migrates to an extreme polar position. We have now characterized the sequences required for this migration. We show that the previously characterized soj-spo0J chromosome segregation system is not essential for chromosome movement to the cell pole, so this must be driven by an additional segregation mechanism. Observations on a large set of precisely engineered chromosomal inversions and translocations have identified a polar localization region (PLR), which lies approximately 150-300 kbp to the left of oriC. Surprisingly, oriC itself has no involvement in this chromosome segregation system. Dissection of the PLR showed that it has internal functional redundancy, reminiscent of the large diffuse centromeres of most eukaryotic cells.
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Affiliation(s)
| | - Jeff Errington
- Sir William Dunn School of Pathology, University of Oxford, South Parks Road, Oxford OX1 3RE, UK
Corresponding author e-mail:
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92
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Corre J, Louarn JM. Evidence from terminal recombination gradients that FtsK uses replichore polarity to control chromosome terminus positioning at division in Escherichia coli. J Bacteriol 2002; 184:3801-7. [PMID: 12081949 PMCID: PMC135174 DOI: 10.1128/jb.184.14.3801-3807.2002] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Chromosome dimers in Escherichia coli are resolved at the dif locus by two recombinases, XerC and XerD, and the septum-anchored FtsK protein. Chromosome dimer resolution (CDR) is subject to strong spatiotemporal control: it takes place at the time of cell division, and it requires the dif resolution site to be located at the junction between the two polarized chromosome arms or replichores. Failure of CDR results in trapping of DNA by the septum and RecABCD recombination (terminal recombination). We had proposed that dif sites of a dimer are first moved to the septum by mechanisms based on local polarity and that normally CDR then occurs as the septum closes. To determine whether FtsK plays a role in the mobilization process, as well as in the recombination reaction, we characterized terminal recombination in an ftsK mutant. The frequency of recombination at various points in the terminus region of the chromosome was measured and compared with the recombination frequency on a xerC mutant chromosome with respect to intensity, the region affected, and response to polarity distortion. The use of a prophage excision assay, which allows variation of the site of recombination and interference with local polarity, allowed us to find that cooperating FtsK-dependent and -independent processes localize dif at the septum and that DNA mobilization by FtsK is oriented by the polarity probably due to skewed sequence motifs of the mobilized material.
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Affiliation(s)
- Jacqueline Corre
- Laboratoire de Microbiologie et de Génétique Moléculaires, CNRS, 31062 Toulouse Cedex, France
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93
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Woldringh CL. The role of co-transcriptional translation and protein translocation (transertion) in bacterial chromosome segregation. Mol Microbiol 2002; 45:17-29. [PMID: 12100545 DOI: 10.1046/j.1365-2958.2002.02993.x] [Citation(s) in RCA: 190] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Many recent reviews in the field of bacterial chromosome segregation propose that newly replicated DNA is actively separated by the functioning of specific proteins. This view is primarily based on an interpretation of the position of fluorescently labelled DNA regions and proteins in analogy to the active segregation mechanism in eukaryotic cells, i.e. to mitosis. So far, physical aspects of DNA organization such as the diffusional movement of DNA supercoil segments and their interaction with soluble proteins, leading to a phase separation between cytoplasm and nucleoid, have received relatively little attention. Here, a quite different view is described taking into account DNA-protein interactions, the large variation in the cellular position of fluorescent foci and the compaction and fusion of segregated nucleoids upon inhibition of RNA or protein synthesis. It is proposed that the random diffusion of DNA supercoil segments is transiently constrained by the process of co- transcriptional translation and translocation (transertion) of membrane proteins. After initiation of DNA replication, a bias in the positioning of transertion areas creates a bidirectionality in chromosome segregation that becomes self-enhanced when neighbouring genes on the same daughter chromosome are expressed. This transertion-mediated segregation model is applicable to multifork replication during rapid growth and to multiple chromosomes and plasmids that occur in many bacteria.
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Affiliation(s)
- Conrad L Woldringh
- Swammerdam Institute for Life Sciences, BioCentrum Amsterdam, University of Amsterdam, The Netherlands.
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94
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Abstract
The mechanisms responsible for prokaryotic DNA segregation are largely unknown. The partitioning locus (par) encoded by the Escherichia coli plasmid R1 actively segregates its replicon to daughter cells. We show here that the ParM ATPase encoded by par forms dynamic actin-like filaments with properties expected for a force-generating protein. Filament formation depended on the other components encoded by par, ParR and the centromere-like parC region to which ParR binds. Mutants defective in ParM ATPase exhibited hyperfilamentation and did not support plasmid partitioning. ParM polymerization was ATP dependent, and depolymerization of ParM filaments required nucleotide hydrolysis. Our in vivo and in vitro results indicate that ParM polymerization generates the force required for directional movement of plasmids to opposite cell poles and that the ParR-parC complex functions as a nucleation point for ParM polymerization. Hence, we provide evidence for a simple prokaryotic analogue of the eukaryotic mitotic spindle apparatus.
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Affiliation(s)
| | - Rasmus Bugge Jensen
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark and
MRC Laboratory of Molecular Biology, Hills Road, Cambridge CB2 2QH, UK Present address: Genencor International Inc., 925 Page Mill Road, Palo Alto, CA 94304-1013, USA Corresponding author e-mail:
| | - Jan Löwe
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark and
MRC Laboratory of Molecular Biology, Hills Road, Cambridge CB2 2QH, UK Present address: Genencor International Inc., 925 Page Mill Road, Palo Alto, CA 94304-1013, USA Corresponding author e-mail:
| | - Kenn Gerdes
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark and
MRC Laboratory of Molecular Biology, Hills Road, Cambridge CB2 2QH, UK Present address: Genencor International Inc., 925 Page Mill Road, Palo Alto, CA 94304-1013, USA Corresponding author e-mail:
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95
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Abstract
DNA topoisomerases are the magicians of the DNA world by allowing DNA strands or double helices to pass through each other, they can solve all of the topological problems of DNA in replication, transcription and other cellular transactions. Extensive biochemical and structural studies over the past three decades have provided molecular models of how the various subfamilies of DNA topoisomerase manipulate DNA. In this review, the cellular roles of these enzymes are examined from a molecular point of view.
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Affiliation(s)
- James C Wang
- Department of Molecular and Cellular Biology, Harvard University, Fairchild Building, 7 Divinity Avenue, Cambridge, Massachusetts 02138, USA.
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96
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Dubessay P, Ravel C, Bastien P, Stuart K, Dedet JP, Blaineau C, Pagès M. Mitotic stability of a coding DNA sequence-free version of Leishmania major chromosome 1 generated by targeted chromosome fragmentation. Gene 2002; 289:151-9. [PMID: 12036593 DOI: 10.1016/s0378-1119(02)00506-1] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The deletion of a 260-kb segment containing all the coding DNA sequences (CDS) of chromosome 1 of Leishmania major Friedlin strain was performed through homologous recombination during a transfection experiment. This allowed the selection of a mutant clone containing a linear extra chromosome sizing 155 kb (XC155). The structure of XC155 was determined by restriction analysis and DNA cloning and sequencing of the gel-purified chromosome: it is made of a 'mirror' inverted duplication of the 'right' end of chromosome 1a (approximately 25 kb at each end), and in its central part of a complex tandem amplification of the linearized transfection vector containing the hygromycin resistance gene (over approximately 105 kb). No sequence of the coding region of chromosome 1 (including the 1.6-kb 'switch' region) was found. By contrast, XC155 contains two large (approximately 13 kb) clusters of tandemly repeated subtelomeric sequences (272-bp 'satellite' DNA) as well as telomeric hexamer repeats. This extra chromosome was found to be mitotically stable after >150 generations without selective pressure in vitro. Two sequence elements are considered which may have an effect on mitotic stability and participate to centromeric function in this extra chromosome: the amplification of the input vector and the 272-bp 'satellite' DNA bound by telomeric repeats.
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Affiliation(s)
- Pascal Dubessay
- CNRS UMR5093 Génome et Biologie Moléculaire des Protozoaires Parasites, Laboratoire de Parasitologie-Mycologie, Faculté de Médecine, 163 Rue A. Broussonet, F-34090 Montpellier, France
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97
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Ho TQ, Zhong Z, Aung S, Pogliano J. Compatible bacterial plasmids are targeted to independent cellular locations in Escherichia coli. EMBO J 2002; 21:1864-72. [PMID: 11927570 PMCID: PMC125944 DOI: 10.1093/emboj/21.7.1864] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Targeting of DNA molecules to specific subcellular positions is essential for efficient segregation, but the mechanisms underlying these processes are poorly understood. In Escherichia coli, several plasmids belonging to different incompatibility groups (F, P1 and RK2) localize preferentially near the midcell and quartercell positions. Here we compare the relative positions of these three plasmids using fluorescence in situ hybridization. When plasmids F and P1 were localized simultaneously using differentially labeled probes, the majority of foci (approximately 75%) were well separated from each other. Similar results were found when we compared the subcellular localization of F with RK2, and RK2 with P1: regardless of the number of foci per cell or growth conditions, most of the foci (70-80%) were not in close proximity to one another. We also localized RK2 in Pseudomonas aeruginosa and Vibrio cholerae, and found that plasmid RK2 localization is conserved across bacterial species. Our results suggest that each plasmid has its own unique subcellular address, implying a mechanism for the stable co-existence of plasmids in which subcellular targeting plays a major role.
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Affiliation(s)
| | | | | | - Joe Pogliano
- Division of Biology, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0322, USA
Corresponding author e-mail:
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98
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Gordon GS, Shivers RP, Wright A. Polar localization of the Escherichia coli oriC region is independent of the site of replication initiation. Mol Microbiol 2002; 44:501-7. [PMID: 11972786 DOI: 10.1046/j.1365-2958.2002.02901.x] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The location of the origin-linked region of the Escherichia coli chromosome was analysed in strains lacking the core origin locus, oriC. In these strains, which initiate replication from F factors integrated at different locations around the chromosome, origin-linked DNA remains localized near the cell poles, as in wild-type cells. In contrast, minichromosomes containing 7 kb of chromosomal DNA including oriC are generally excluded from the ends of the cell. Thus, we propose that positioning of the wild-type origins at the poles is not a function of their order of replication but a sequence-specific phenomenon. It is proposed that there are centromere-like sequences, bordering the wild-type origin of replication, which are used by host mechanisms to direct the proper placement of the origin region of the chromosome. This function, combined with other host processes, may assure efficient segregation of the E. coli chromosome.
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Affiliation(s)
- G Scott Gordon
- Department of Molecular Biology and Microbiology, Tufts University School of Medicine, 136 Harrison Avenue, Boston, MA 02111, USA
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99
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Siddique A, Figurski DH. The active partition gene incC of IncP plasmids is required for stable maintenance in a broad range of hosts. J Bacteriol 2002; 184:1788-93. [PMID: 11872733 PMCID: PMC134889 DOI: 10.1128/jb.184.6.1788-1793.2002] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Plasmids of incompatibility group P (IncP) are capable of replication and stable inheritance in a wide variety of gram-negative bacteria. Three determinants of IncP plasmids are components of an active partition locus that is predicted to function in the segregation of plasmid copies to daughter cells. These determinants are incC, which codes for a member of the ParA family of partition ATPases; korB, which specifies a DNA-binding protein that also functions as a global transcriptional repressor; and O(B), the DNA target for KorB, which occurs at multiple locations on IncP plasmids. To determine the importance and host range of the IncC/KorB partition system in the maintenance of IncP plasmids, we constructed an in-frame deletion of incC in the otherwise intact 60-kb IncP alpha plasmid R995. R995 Delta incC was found to be highly unstable in Escherichia coli, Pseudomonas aeruginosa, Pseudomonas putida, Agrobacterium tumefaciens, and Acinetobacter calcoaceticus, whereas wild-type R995 is stable in all these hosts. In addition, R995 Delta incC could not be established in Actinobacillus actinomycetemcomitans. trans-Complementation analysis showed that the coding region for IncC2 polypeptide, which is expressed from an internal translational start within the incC gene, was sufficient to restore stable maintenance to wild-type levels. The results show that the IncC/KorB active partition system of IncP plasmids is remarkably proficient for stable maintenance in diverse bacteria.
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Affiliation(s)
- Azeem Siddique
- Department of Microbiology, College of Physicians and Surgeons, Columbia University, New York, New York 10032, USA
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100
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Ebersbach G, Gerdes K. The double par locus of virulence factor pB171: DNA segregation is correlated with oscillation of ParA. Proc Natl Acad Sci U S A 2001; 98:15078-83. [PMID: 11752455 PMCID: PMC64986 DOI: 10.1073/pnas.261569598] [Citation(s) in RCA: 115] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Prokaryotic plasmids and chromosomes encode partitioning (par) loci that segregate DNA to daughter cells before cell division. Recent database analyses showed that almost all known par loci encode an ATPase and a DNA-binding protein, and one or more cis-acting regions where the proteins act. All par-encoded ATPases belong to one of two protein superfamilies, Walker-type and actin-like ATPases. This property was recently used to divide par loci into Types I and II loci. We show here that the Escherichia coli virulence factor pB171 encodes a double par locus that consists of one Type I and one Type II locus. Separately, each locus stabilized a test-plasmid efficiently. Together, the two loci mediated even more efficient plasmid stabilization. The par loci have a unique genetic organization in that they share a common central region at which the two different DNA-binding proteins probably act. Interestingly, a fusion protein consisting of the Walker-type ParA ATPase and Gfp was functional and oscillated in nucleoid regions on a time scale of minutes. ParA-green fluorescent protein (Gfp) oscillation depended on both ParB and parC but was independent of minCDE. Point mutations in the Walker A box motif simultaneously abolished plasmid stabilization and ParA-Gfp oscillation. These observations raise the possibility that ParA oscillation is prerequisite for active plasmid segregation.
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Affiliation(s)
- G Ebersbach
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark
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