The SMC complex, MukBEF, organizes the Escherichia coli chromosome by forming an axial core

Abstract

Structural Maintenance of Chromosomes (SMC) complexes organize and individualize chromosomes ubiquitously, thereby contributing to their faithful segregation. Here we explore how Escherichia coli chromosome organization emerges from the action of the SMC complex MukBEF, using quantitative imaging in cells with increased MukBEF occupancy on the chromosome. We demonstrate that the E. coli chromosome is organized as series of loops around a thin axial MukBEF core whose length is ~1100 times shorter than the chromosomal DNA. The core is linear (1 m), or circular (1.5 m) in the absence of MatP, which displaces MukBEF from the 800 kbp replication termination region (ter). Our findings illustrate how MukBEF compacts the chromosome lengthwise and demonstrate how displacement of MukBEF from ter promotes MukBEF enrichment with the replication origin.