Cell Biology

Dividing the Inheritance

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Science  04 Jan 2008:
Vol. 319, Issue 5859, pp. 13
DOI: 10.1126/science.319.5859.13d

Cell division can be a hazardous process for any cell that needs to segregate the two copies of its genome into daughter cells. Prokaryotic cells often harbor extrachromosomal elements, such as plasmids, that also need to be allocated fairly. One well-studied example is the partitioning of the R1 multidrug resistance plasmid in Escherichia coli; this process is powered by the actin-like ATPase ParM. Although ParM has structural homology to actin, in filamentous form, it displays dynamic instability reminiscent of microtubules. Campbell and Mullins have used time-lapse fluorescence microscopy to follow plasmid segregation in E. coli. ParM filaments form spindles that are capable of capturing a plasmid at each end and then pushing them to opposite ends of the cell at about 50 nm/s. Initially, spindles do not always align with the long axis of the cell, but alignment probably occurs during elongation. After reaching the poles, the filaments undergo catastrophic depolymerization. Remarkably, the relocated plasmids do not remain fixed at the poles, and may diffuse and suffer multiple rounds of segregation before cell division. — VV

J. Cell Biol. 179, 1059 (2007).

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