Nonrandom segregation of sister chromosomes by Escherichia coli MukBEF

Abstract

Structural maintenance of chromosomes (SMC) complexes contribute to chromosome organization in all domains of life. In Escherichia coli, MukBEF, the functional SMC homolog, promotes spatiotemporal chromosome organization and faithful chromosome segregation. Here, we address the relative contributions of MukBEF and the replication terminus (ter) binding protein, MatP, to chromosome organization–segregation. We show that MukBEF, but not MatP, is required for the normal localization of the origin of replication to midcell and for the establishment of translational symmetry between newly replicated sister chromosomes. Overall, chromosome orientation is normally maintained through division from one generation to the next. Analysis of loci flanking the replication termination region (ter), which demark the ends of the linearly organized portion of the nucleoid, demonstrates that MatP is required for maintenance of chromosome orientation. We show that DNA-bound β2-processivity clamps, which mark the lagging strands at DNA replication forks, localize to the cell center, independent of replisome location but dependent on MukBEF action, and consistent with translational symmetry of sister chromosomes. Finally, we directly show that the older (“immortal”) template DNA strand, propagated from previous generations, is preferentially inherited by the cell forming at the old pole, dependent on MukBEF and MatP. The work further implicates MukBEF and MatP as central players in chromosome organization, segregation, and nonrandom inheritance of genetic material and suggests a general framework for understanding how chromosome conformation and dynamics shape subcellular organization.

Polymer architecture orchestrates the segregation and spatial organization of replicatingE. colichromosomes in slow growth

“…Alternatively, the CLs may arise due to SMC proteins such as MukBEF which are known to create contacts between segments separated by ∼900 kbp. 32,61 Previous studies already suggest that the E. coli chromosome is organized into ‘loop domains’. 62–64 It has also been shown previously that depletion of some SMC proteins like MukBEF leads to defects in the segregation of the E. coli chromosome, thus underlining their importance.…”

Acyl carrier protein promotes MukBEF action in Escherichia coli chromosome organization-segregation

“…ATPase activity is essential for in vivo function, as mutant MukB proteins that are deficient in ATP hydrolysis (MukB E1407Q , hereafter referred to as Muk-B EQ ) or ATP binding (MukB D1406A , hereafter referred to as MukB DA ) display ΔmukB phenotypes 6,17,18 . Cells lacking functional MukBEF, grown in a minimal medium under permissive conditions, have disorganized chromosomes with misplaced genetic loci, and fail to properly segregate sister chromosomes, leading to anucleate cell production 4,6,[18][19][20] . Furthermore, ΔmukB cells are inviable during rapid growth that supports overlapping replication cycles, apparently because of failures in chromosome segregation 4,6,18,20 .…”

MukBEF-dependent chromosomal organization in widened Escherichia coli

“…MukBEF and MatP are not merely factors that set the density of the chromosome, but they also play a major role in DNA segregation. For instance, MukBEF was recently shown to direct newly replicated origins towards the daughter cells 12 , and as a result, deletion of MukB resulted in anucleated cells and in cells that have unsegregated oriC at the older cell pole. MatP was conversely shown to be necessary for the proper localization of the ter domain after segregation and subsequent cell division 43 and MatP was found to be involved in sister cohesion during the chromosomal movement right before cell division 44 .…”

“…DNA can be bound and re-shaped in vitro by the hinge-like configuration of the MukB subunits in an ATP-dependent manner 10 . Recent studies reported that a 6-fold increase in the number of MukBEF copies led to the formation of a ring-like structure of SMCs along the toroidal nucleoid 11,12 . This ring was hypothesized to function as a chromosomal backbone from which peripheral DNA loops protrude.…”