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MukB colocalizes with the oriC region and is required for organization of the two Escherichia coli chromosome arms into separate cell halves.

Danilova O, Reyes-Lamothe R, Pinskaya M, Sherratt D, Possoz C - Mol. Microbiol. (2007)

Bottom Line: We show that in mukB mutant cells, the two chromosome arms do not separate into distinct cell halves, but extend from pole to pole with the oriC region located at the old pole.Mutations in topA, encoding topoisomerase I, do not suppress the aberrant positioning of chromosomal loci in mukB cells, despite suppressing the temperature-sensitivity and production of anucleate cells.We propose that MukBEF initiates the normal bidirectional organization of the chromosome from the oriC region.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry, University of Oxford, Oxford OX1 3QU, UK.

ABSTRACT
The circular Escherichia coli chromosome is organized by bidirectional replication into two equal left and right arms (replichores). Each arm occupies a separate cell half, with the origin of replication (oriC) at mid-cell. E. coli MukBEF belongs to the ubiquitous family of SMC protein complexes that play key roles in chromosome organization and processing. In mukBEF mutants, viability is restricted to low temperature with production of anucleate cells, reflecting chromosome segregation defects. We show that in mukB mutant cells, the two chromosome arms do not separate into distinct cell halves, but extend from pole to pole with the oriC region located at the old pole. Mutations in topA, encoding topoisomerase I, do not suppress the aberrant positioning of chromosomal loci in mukB cells, despite suppressing the temperature-sensitivity and production of anucleate cells. Furthermore, we show that MukB and the oriC region generally colocalize throughout the cell cycle, even when oriC localization is aberrant. We propose that MukBEF initiates the normal bidirectional organization of the chromosome from the oriC region.

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Related in: MedlinePlus

Model of E. coli chromosome organization/segregation. Wild-type: Chromosomes segregation is facilitated by the <L-R> organization initiated by MukB colocalizing with the ori regions. mukB (22°C) and mukB topA10: ‘MukB-free’ segregation is allowed only when the level of negative DNA supercoiling is increased (low temperature/topA10) but leads to an aberrant arrangement, with the two arms extending (twisted or not with each other) from the old poles to the new poles. For clarity, the two replichores are represented as untwisted. The chromosome organization in mukB topA10 cells is extrapolated from the aberrant origin positioning.
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fig05: Model of E. coli chromosome organization/segregation. Wild-type: Chromosomes segregation is facilitated by the <L-R> organization initiated by MukB colocalizing with the ori regions. mukB (22°C) and mukB topA10: ‘MukB-free’ segregation is allowed only when the level of negative DNA supercoiling is increased (low temperature/topA10) but leads to an aberrant arrangement, with the two arms extending (twisted or not with each other) from the old poles to the new poles. For clarity, the two replichores are represented as untwisted. The chromosome organization in mukB topA10 cells is extrapolated from the aberrant origin positioning.

Mentions: We consider three types of mechanism that could give rise to the observations of MukB-ori colocalization. The first involves a direct interaction of MukBEF with some feature of the ori region (Fig. 5). This could relate to some sequence motif(s) present in the ori region, or to some other aspect of ori biology. Alternatively, the ori region and MukBEF could be targeted by independent mechanisms to the same cellular compartment. This seems unlikely, given that MukB clusters still colocalize with ori1 when it is positioned aberrantly. A third possible mechanism is a rosette model in which MukBEF molecules bind discrete sites spread over the chromosome (for example, one per topological domain), and MukBEF–MukBEF interactions lead to a rosette-like structure, centred on the origin region.


MukB colocalizes with the oriC region and is required for organization of the two Escherichia coli chromosome arms into separate cell halves.

Danilova O, Reyes-Lamothe R, Pinskaya M, Sherratt D, Possoz C - Mol. Microbiol. (2007)

Model of E. coli chromosome organization/segregation. Wild-type: Chromosomes segregation is facilitated by the <L-R> organization initiated by MukB colocalizing with the ori regions. mukB (22°C) and mukB topA10: ‘MukB-free’ segregation is allowed only when the level of negative DNA supercoiling is increased (low temperature/topA10) but leads to an aberrant arrangement, with the two arms extending (twisted or not with each other) from the old poles to the new poles. For clarity, the two replichores are represented as untwisted. The chromosome organization in mukB topA10 cells is extrapolated from the aberrant origin positioning.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2169520&req=5

fig05: Model of E. coli chromosome organization/segregation. Wild-type: Chromosomes segregation is facilitated by the <L-R> organization initiated by MukB colocalizing with the ori regions. mukB (22°C) and mukB topA10: ‘MukB-free’ segregation is allowed only when the level of negative DNA supercoiling is increased (low temperature/topA10) but leads to an aberrant arrangement, with the two arms extending (twisted or not with each other) from the old poles to the new poles. For clarity, the two replichores are represented as untwisted. The chromosome organization in mukB topA10 cells is extrapolated from the aberrant origin positioning.
Mentions: We consider three types of mechanism that could give rise to the observations of MukB-ori colocalization. The first involves a direct interaction of MukBEF with some feature of the ori region (Fig. 5). This could relate to some sequence motif(s) present in the ori region, or to some other aspect of ori biology. Alternatively, the ori region and MukBEF could be targeted by independent mechanisms to the same cellular compartment. This seems unlikely, given that MukB clusters still colocalize with ori1 when it is positioned aberrantly. A third possible mechanism is a rosette model in which MukBEF molecules bind discrete sites spread over the chromosome (for example, one per topological domain), and MukBEF–MukBEF interactions lead to a rosette-like structure, centred on the origin region.

Bottom Line: We show that in mukB mutant cells, the two chromosome arms do not separate into distinct cell halves, but extend from pole to pole with the oriC region located at the old pole.Mutations in topA, encoding topoisomerase I, do not suppress the aberrant positioning of chromosomal loci in mukB cells, despite suppressing the temperature-sensitivity and production of anucleate cells.We propose that MukBEF initiates the normal bidirectional organization of the chromosome from the oriC region.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry, University of Oxford, Oxford OX1 3QU, UK.

ABSTRACT
The circular Escherichia coli chromosome is organized by bidirectional replication into two equal left and right arms (replichores). Each arm occupies a separate cell half, with the origin of replication (oriC) at mid-cell. E. coli MukBEF belongs to the ubiquitous family of SMC protein complexes that play key roles in chromosome organization and processing. In mukBEF mutants, viability is restricted to low temperature with production of anucleate cells, reflecting chromosome segregation defects. We show that in mukB mutant cells, the two chromosome arms do not separate into distinct cell halves, but extend from pole to pole with the oriC region located at the old pole. Mutations in topA, encoding topoisomerase I, do not suppress the aberrant positioning of chromosomal loci in mukB cells, despite suppressing the temperature-sensitivity and production of anucleate cells. Furthermore, we show that MukB and the oriC region generally colocalize throughout the cell cycle, even when oriC localization is aberrant. We propose that MukBEF initiates the normal bidirectional organization of the chromosome from the oriC region.

Show MeSH
Related in: MedlinePlus