How is DNA compacted >1000-fold lengthwise to form a chromosome?

MukBEF – Structural Maintenance of Chromosomes (SMC) complex
(Click image to enlarge)

Jarno Mäkelä and David Sherratt show how the chromosome is organized within a bacterial cell in a paper published in Molecular Cell this February (DOI:10.1016/j.molcel.2020.02.003).

In all organisms, DNA is compacted >1000-fold lengthwise to form chromosomes, in order that they can be appropriately positioned and execute their functions in a cell. By using super-resolution and quantitative live-cell imaging, genetics and modelling, Jarno Mäkelä has shown that in E. coli, the SMC complex, MukBEF, organizes the 4.6 Mbp circular chromosome, using ATP hydrolysis to form an axial core from which loops of size 20-50 kb emanate. MukBEF binds randomly to all chromosome regions, from where it is proposed that it extrudes DNA loops. When MukBEF encounters the ~800 bp replication termination region (ter), its interaction with MatP bound to ~23 matS sites within ter, leads to its dissociation from ter. This depletion directs an enrichment of MukBEF complexes at the replication origin region (ori) and ensures that the two chromosome arms are segregation to opposite cell halves.



  1. Molecular Cell paper:


David Sherratt
2nd March 2020