Towards understanding the molecular basis of bacterial DNA segregation

Abstract

Bacteria ensure the fidelity of genetic inheritance by the coordinated control of chromosome segregation and cell division. Here, we review the molecules and mechanisms that govern the correct subcellular positioning and rapid separation of newly replicated chromosomes and plasmids towards the cell poles and, significantly, the emergence of mitotic-like machineries capable of segregating plasmid DNA. We further describe surprising similarities between proteins involved in DNA partitioning (ParA/ParB) and control of cell division (MinD/MinE), suggesting a mechanism for intracellular positioning common to the two processes. Finally, we discuss the role that the bacterial cytoskeleton plays in DNA partitioning and the missing link between prokaryotes and eukaryotes that is bacterial mechano-chemical motor proteins.

Figure 1

Model of ‘assisted treadmilling’ of ParA-like proteins. Soj (ParA) binds to DNA in its ATP-dependent dimeric form. Because the nucleotide is almost completely occluded in the ‘sandwich dimer’ of Soj, there is probably very little nucleotide exchange in and out of the nucleoprotein filament—a pre-requisite for the two ends of the filament being different. Spo0J (ParB) enhances Soj ATP hydrolysis and, therefore, can chase Soj off the DNA. The result is treadmilling of Soj assisted by the N-terminal residues of Spo0J. The result is a relative movement of Soj/Spo0J against the DNA, and this movement could be used in various ways depending on what is more stationary in the cell. Note that a similar mechanism involving membrane-associated polymerization can be proposed for MinD (replacing Soj) and MinE (replacing Spo0J).