NORMAL GENOMIC

• Bigot S, Sivanathan V, Possoz C, Barre FX, Cornet F
• FtsK, a literate chromosome segregation machine.
• Mol Microbiol. 2007; 64: 1434-41
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• The study of chromosome segregation in bacteria has gained strong insightsfrom the use of cytology techniques. A global view of chromosomechoreography during the cell cycle is emerging, highlighting as a nextchallenge the description of the molecular mechanisms and factorsinvolved. Here, we review one of such factor, the FtsK DNA translocase.FtsK couples segregation of the chromosome terminus, the ter region, withcell division. It is a powerful and fast translocase that reads chromosomepolarity to find the end, thereby sorting sister ter regions on eitherside of the division septum, and activating the last steps of segregation.Recent data have revealed the structure of the FtsK motor, howtranslocation is oriented by specific DNA motifs, termed KOPS, andsuggests novel mechanisms for translocation and sensing chromosomepolarity.

• Grainge I, Bregu M, Vazquez M, Sivanathan V, Ip SC, Sherratt DJ
• Unlinking chromosome catenanes in vivo by site-specific recombination.
• EMBO J. 2007; 26: 4228-38
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• A challenge for chromosome segregation in all domains of life is theformation of catenated progeny chromosomes, which arise during replicationas a consequence of the interwound strands of the DNA double helix.Topoisomerases play a key role in DNA unlinking both during and at thecompletion of replication. Here we report that chromosome unlinking caninstead be accomplished by multiple rounds of site-specific recombination.We show that step-wise, site-specific recombination by XerCD-dif orCre-loxP can unlink bacterial chromosomes in vivo, in reactions thatrequire KOPS-guided DNA translocation by FtsK. Furthermore, we show thatoverexpression of a cytoplasmic FtsK derivative is sufficient to allowchromosome unlinking by XerCD-dif recombination when either subunit ofTopoIV is inactivated. We conclude that FtsK acts in vivo to simplifychromosomal topology as Xer recombination interconverts monomeric anddimeric chromosomes.

• Ptacin JL, Nollmann M, Bustamante C, Cozzarelli NR
• Identification of the FtsK sequence-recognition domain.
• Nat Struct Mol Biol. 2006; 13: 1023-5
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• FtsK is a prokaryotic multidomain DNA translocase that coordinateschromosome segregation and cell division. FtsK is membrane anchored at thedivision septum and, guided by highly skewed DNA sequences, translocatesthe chromosome to bring the terminus of replication to the septum. Here,we use in vitro single-molecule and ensemble methods to unveil a mechanismof action in which the translocation and sequence-recognition activitiesare performed by different domains in FtsK.

• Bigot S, Saleh OA, Cornet F, Allemand JF, Barre FX
• Oriented loading of FtsK on KOPS.
• Nat Struct Mol Biol. 2006; 13: 1026-8
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• In Escherichia coli, the ATP-dependent DNA translocase FtsK transports DNAacross the site of cell division and activates recombination by the XerCDrecombinases at a specific site on the chromosome, dif, to ensure the laststages of chromosome segregation. DNA transport by FtsK is oriented by8-base-pair asymmetric sequences ('KOPS'). Here we provide evidence thatKOPS promote FtsK loading on DNA and that translocation is oriented atthis step.

• Strick TR, Quessada-Vial A
• FtsK: a groovy helicase.
• Nat Struct Mol Biol. 2006; 13: 948-50

• Massey TH, Mercogliano CP, Yates J, Sherratt DJ, Lowe J
• Double-stranded DNA translocation: structure and mechanism of hexamericFtsK.
• Mol Cell. 2006; 23: 457-69
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• FtsK is a DNA translocase that coordinates chromosome segregation and celldivision in bacteria. In addition to its role as activator of XerCDsite-specific recombination, FtsK can translocate double-stranded DNA(dsDNA) rapidly and directionally and reverse direction. We presentcrystal structures of the FtsK motor domain monomer, showing that it has aRecA-like core, the FtsK hexamer, and also showing that it is a ring witha large central annulus and a dodecamer consisting of two hexamers, headto head. Electron microscopy (EM) demonstrates the DNA-dependent existenceof hexamers in solution and shows that duplex DNA passes through themiddle of each ring. Comparison of FtsK monomer structures from twodifferent crystal forms highlights a conformational change that we proposeis the structural basis for a rotary inchworm mechanism of DNAtranslocation.

• Bigot S et al.
• KOPS: DNA motifs that control E. coli chromosome segregation by orientingthe FtsK translocase.
• EMBO J. 2005; 24: 3770-80
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• Bacterial chromosomes are organized in replichores of opposite sequencepolarity. This conserved feature suggests a role in chromosome dynamics.Indeed, sequence polarity controls resolution of chromosome dimers inEscherichia coli. Chromosome dimers form by homologous recombinationbetween sister chromosomes. They are resolved by the combined action oftwo tyrosine recombinases, XerC and XerD, acting at a specific chromosomalsite, dif, and a DNA translocase, FtsK, which is anchored at the divisionseptum and sorts chromosomal DNA to daughter cells. Evidences suggest thatDNA motifs oriented from the replication origin towards dif provide FtsKwith the necessary information to faithfully distribute chromosomal DNA toeither side of the septum, thereby bringing the dif sites together at theend of this process. However, the nature of the DNA motifs acting as FtsKorienting polar sequences (KOPS) was unknown. Using genetics,bioinformatics and biochemistry, we have identified a family of DNA motifsin the E. coli chromosome with KOPS activity.

• Corre J, Louarn JM
• Extent of the activity domain and possible roles of FtsK in theEscherichia coli chromosome terminus.
• Mol Microbiol. 2005; 56: 1539-48
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• Escherichia coli FtsK protein couples cell division and chromosomesegregation. It is a component of the septum essential for cell division.It also acts during chromosome dimer resolution by XerCD-specificrecombination at the dif site, with two distinct activities: DNAtranslocation oriented by skewed sequence elements and direct activationof Xer recombination. Dimer resolution requires that the skewed elementspolarize in opposite directions 30-50 kb on either side of dif. Thisconstitutes the DIF domain, approximately coincident with the region wherereplication terminates. The observation that the ftsK1 mutation increasesrecombination near dif was exploited to determine whether the chromosomeregion on which FtsK acts is limited to the DIF domain. A monitoring ofrecombination activity at multiple loci in a 350 kb region to the left ofdif revealed (i) zones of differing activities unconnected to dimerresolution and (ii) a constant 10-fold increase of recombination in the250 kb region adjacent to dif in the ftsK1 mutant. The latter effectallows definition of an FTSK domain whose total size is at least fourfoldthat of the DIF domain. Additional analyses revealed that FtsK activityresponds to polarization in the whole FTSK domain and that displacement ofthe region where replication terminates preserves differences betweenrecombination zones. Our interpretation is that translocation by FtsKoccurs mostly on DNA belonging to a specifically organized domain of thechromosome, when physical links between either dimeric or stillintercatenated chromosomes force this DNA to run across the septum atdivision.

• Bigot S, Corre J, Louarn JM, Cornet F, Barre FX
• FtsK activities in Xer recombination, DNA mobilization and cell divisioninvolve overlapping and separate domains of the protein.
• Mol Microbiol. 2004; 54: 876-86
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• Escherichia coli FtsK is a multifunctional protein that couples celldivision and chromosome segregation. Its N-terminal transmembrane domain(FtsK(N)) is essential for septum formation, whereas its C-terminal domain(FtsK(C)) is required for chromosome dimer resolution by XerCD-difsite-specific recombination. FtsK(C) is an ATP-dependent DNA translocase.In vitro and in vivo data point to a dual role for this domain inchromosome dimer resolution (i) to directly activate recombination byXerCD-dif and (ii) to bring recombination sites together and/or to clearDNA from the closing septum. FtsK(N) and FtsK(C) are separated by a longlinker region (FtsK(L)) of unknown function that is highly divergentbetween bacterial species. Here, we analysed the in vivo effects ofdeletions of FtsK(L) and/or of FtsK(C), of swaps of these domains withtheir Haemophilus influenzae counterparts and of a point mutation thatinactivates the walker A motif of FtsK(C). Phenotypic characterization ofthe mutants indicated a role for FtsK(L) in cell division. Moreimportantly, even though Xer recombination activation and DNA mobilizationboth rely on the ATPase activity of FtsK(C), mutants were found that canperform only one or the other of these two functions, which allowed theirseparation in vivo for the first time.

• Ip SC, Bregu M, Barre FX, Sherratt DJ
• Decatenation of DNA circles by FtsK-dependent Xer site-specificrecombination.
• EMBO J. 2003; 22: 6399-407
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• DNA replication results in interlinked (catenated) sister duplex moleculesas a consequence of the intertwined helices that comprise duplex DNA. DNAtopoisomerases play key roles in decatenation. We demonstrate a novel,efficient and directional decatenation process in vitro, which uses thecombination of the Escherichia coli XerCD site-specific recombinationsystem and a protein, FtsK, which facilitates simple synapsis of difrecombination sites during its translocation along DNA. We propose thatthe FtsK-XerCD recombination machinery, which converts chromosomal dimersto monomers, may also function in vivo in removing the final catenationlinks remaining upon completion of DNA replication.