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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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Mispositioned or non-duplicating ori1 foci colocalize with MukB. A. topA10 cells (OS70) containing more than two ori1 (left) or containing a polar ori1 (right).B. Wild-type cells after 3 h of rifampicin treatment with tetO array inserted at either position ori1 (left, OS29 cells; see Fig. 3 for the histogram legend) or R2 (right, OS69 cells).C. dnaCts cells (OS82) grown at 37°C for 8 h with tetO at ori1. The percentages in panels A, B and C refer to the colocalization of ori1 or R2 loci with MukB clusters, as deduced from the examination of at least 400 cells.
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fig04: Mispositioned or non-duplicating ori1 foci colocalize with MukB. A. topA10 cells (OS70) containing more than two ori1 (left) or containing a polar ori1 (right).B. Wild-type cells after 3 h of rifampicin treatment with tetO array inserted at either position ori1 (left, OS29 cells; see Fig. 3 for the histogram legend) or R2 (right, OS69 cells).C. dnaCts cells (OS82) grown at 37°C for 8 h with tetO at ori1. The percentages in panels A, B and C refer to the colocalization of ori1 or R2 loci with MukB clusters, as deduced from the examination of at least 400 cells.

Mentions: In order to test whether MukB positioning depends on ori1 location, the relative MukB and ori1 positioning were analysed in topA10 mutant cells grown at 30°C, where aberrant origin positioning occurs (Fig. 1A and 35% of origins are positioned at a nucleoid edge). Colocalization of a polar ori1 focus with a MukB cluster was substantial in normal-length cells (62%, Fig. 4A). Furthermore, the colocalization was maintained (89%) in the 48% of filamentous cells containing more than two ori1 foci (Fig. 1).


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)

Mispositioned or non-duplicating ori1 foci colocalize with MukB. A. topA10 cells (OS70) containing more than two ori1 (left) or containing a polar ori1 (right).B. Wild-type cells after 3 h of rifampicin treatment with tetO array inserted at either position ori1 (left, OS29 cells; see Fig. 3 for the histogram legend) or R2 (right, OS69 cells).C. dnaCts cells (OS82) grown at 37°C for 8 h with tetO at ori1. The percentages in panels A, B and C refer to the colocalization of ori1 or R2 loci with MukB clusters, as deduced from the examination of at least 400 cells.
© Copyright Policy
Related In: Results  -  Collection

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

fig04: Mispositioned or non-duplicating ori1 foci colocalize with MukB. A. topA10 cells (OS70) containing more than two ori1 (left) or containing a polar ori1 (right).B. Wild-type cells after 3 h of rifampicin treatment with tetO array inserted at either position ori1 (left, OS29 cells; see Fig. 3 for the histogram legend) or R2 (right, OS69 cells).C. dnaCts cells (OS82) grown at 37°C for 8 h with tetO at ori1. The percentages in panels A, B and C refer to the colocalization of ori1 or R2 loci with MukB clusters, as deduced from the examination of at least 400 cells.
Mentions: In order to test whether MukB positioning depends on ori1 location, the relative MukB and ori1 positioning were analysed in topA10 mutant cells grown at 30°C, where aberrant origin positioning occurs (Fig. 1A and 35% of origins are positioned at a nucleoid edge). Colocalization of a polar ori1 focus with a MukB cluster was substantial in normal-length cells (62%, Fig. 4A). Furthermore, the colocalization was maintained (89%) in the 48% of filamentous cells containing more than two ori1 foci (Fig. 1).

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