Chromosome segregation in Escherichia coli involves DNA binding by the MinC-MinD complex

Abstract

The Escherichia coli Min system, composed of the proteins MinC, MinD, and MinE, is crucial for directing septum formation at mid-cell. MinD has also been shown to bind DNA in a non-sequence-specific manner and to tether plasmid DNA to liposomes. A role for the Min system in chromosome segregation has been proposed, whereby repeated, transient membrane-tethering events mediated by MinD could help prevent backward movements of the duplicated chromosomes once entropic forces weaken. However, the contribution of the other Min proteins to DNA binding has remained unclear. Here, we demonstrate that DNA binding is strongly enhanced when MinD and MinC form a complex, while MinE and FtsZ (at high concentrations) interfere with this binding. We reveal a critical role for the linker connecting MinCs N- and C-terminal domains in both DNA binding and inhibition of FtsZ polymerization. E. coli strains expressing MinC linker variants from the native locus, in combination with the alpha subunit of HU tagged with GFP, display chromosomes that appear more spread throughout the cell. This phenotype could reflect reduced compaction, chromosome segregation defects, or a combination of both. These findings suggest a previously unrecognized role for the MinC linker in DNA binding and provide new insights into a potential physiological role of MinCD-DNA bnding in chromosome organization and/or dynamics.