A Bipolar Spindle of Antiparallel ParM Filaments Drives Bacterial Plasmid Segregation

Abstract

Plasmid Partitioning Bacterial plasmids need to be able to partition faithfully into daughter cells. Combining structural data and advanced microscopy, Gayathri et al. (p. 1334 , published online 25 October; see the cover) describe how actin-like ParM filaments form a bipolar spindle for the faithful segregation of low-copy-number plasmids to the two cell poles of Escherichia coli , despite being polar, with two distinct ends. ParM filaments are elongated by a small adaptor protein ParR that physically links the filament end(s) to a centromere-like region on the plasmid. Antiparallel filament bundling and sliding appear to produce a bipolar spindle made of filaments that elongate unidirectionally so that all the plasmids are segregated together in one large bundle.