Self-organised segregation of bacterial chromosomal origins.

Abstract

The chromosomal replication origin region (<i>ori</i>) of characterised bacteria is dynamically positioned throughout the cell cycle. In slowly growing <i>Escherichia coli</i>, <i>ori</i> is maintained at mid-cell from birth until its replication, after which newly replicated sister <i>ori</i>s move to opposite quarter positions. Here, we provide an explanation for <i>ori</i> positioning based on the self-organisation of the Structural Maintenance of Chromosomes complex, MukBEF, which forms dynamically positioned clusters on the chromosome. We propose that a non-trivial feedback between the self-organising gradient of MukBEF complexes and the <i>ori</i>s leads to accurate <i>ori</i> positioning. We find excellent agreement with quantitative experimental measurements and confirm key predictions. Specifically, we show that <i>ori</i>s exhibit biased motion towards MukBEF clusters, rather than mid-cell. Our findings suggest that MukBEF and <i>ori</i>s act together as a self-organising system in chromosome organisation-segregation and introduces protein self-organisation as an important consideration for future studies of chromosome dynamics.