Plasmid segregation: spatial awareness at the molecular level

Abstract

In bacteria, low-copy number plasmids ensure their stable inheritance by partition loci (par), which actively distribute plasmid replicates to each side of the cell division plane. Using time-lapse fluorescence microscopic tracking of segregating plasmid molecules, a new study provides novel insight into the workings of the par system from Escherichia coli plasmid R1. Despite its relative simplicity, the plasmid partition spindle shares characteristics with the mitotic machinery of eukaryotic cells.

Figure 1.

Cartoon showing how ParR–parC DNA complexes interact with opposite ends of a growing ParM filament. The ParR N-terminal ribbon-helix-helix domain binds specifically to parC DNA (red), and the ParR C terminus interacts with ParM-ATP (blue) at or near the filament tips. ATP hydrolysis is proposed to induce a structural rearrangement in ParM that leads to the dislodging of ParR, which, in turn, can reassociate further outwards on the filament that consists of ParM-ATP. The figure was adapted from Møller-Jensen et al. (2007).