The role of co‐transcriptional translation and protein translocation (transertion) in bacterial chromosome segregation

Abstract

Summary Many recent reviews in the field of bacterial chromosome segregation propose that newly replicated DNA is actively separated by the functioning of specific proteins. This view is primarily based on an interpretation of the position of fluorescently labelled DNA regions and proteins in analogy to the active segregation mechanism in eukaryotic cells, i.e. to mitosis. So far, physical aspects of DNA organization such as the diffusional movement of DNA supercoil segments and their interaction with soluble proteins, leading to a phase separation between cytoplasm and nucleoid, have received relatively little attention. Here, a quite different view is described taking into account DNA–protein interactions, the large variation in the cellular position of fluorescent foci and the compaction and fusion of segregated nucleoids upon inhibition of RNA or protein synthesis. It is proposed that the random diffusion of DNA supercoil segments is transiently constrained by the process of co‐ transcriptional translation and translocation (transertion) of membrane proteins. After initiation of DNA replication, a bias in the positioning of transertion areas creates a bidirectionality in chromosome segre‐gation that becomes self‐enhanced when neigh‐bouring genes on the same daughter chromosome are expressed. This transertion‐mediated segregation model is applicable to multifork replication during rapid growth and to multiple chromosomes and plasmids that occur in many bacteria.

Quality matters: how does mitochondrial network dynamics and quality control impact on mtDNA integrity?

“…Instead, the spatial confinement to a cristae microcompartment (if attached to the inner mitochondrial membrane) or the intercristae compartment (if confined by diffusion to specific matrix sections) automatically generates such a link (figure 5). Furthermore, originally, it was proposed that transcription, translation and membrane insertion of proteins are coupled in mitochondria via a process known in bacteria as transertion [88]. The tight spatial arrangement of stacks of cristae together with the compartment character of individual cristae and intercristae space also lifts the requirement for this assumption.…”

Independent Segregation of the Two Arms of theEscherichia coli oriRegion Requires neither RNA Synthesis nor MreB Dynamics

“…As both transcription and the insertion of newly transcribed-translated proteins into membrane (transertion) have been implicated as mechanisms contributing to bacterial chromosome segregation (12,31,45,49,61), we wished to test the consequence of inhibiting transcription (and thereby ongoing transertion) on segregation of ori loci. To do so, we synchronized cells for DNA synthesis using dnaC(Ts) mutation (40) and treated them with rifampin (300 g/ml) to block transcription.…”

“…In a different model, both transcription itself and the coordinated transcription of membrane proteins and their insertion into the membrane ("transertion") have been proposed as processes that can drive chromosome segregation (12,45,49,61). Nevertheless, these proposals have not been tested rigorously by experiments.…”

The bacterial nucleoid: A highly organized and dynamic structure

“…It is conceivable that polymerization reactions and DNA condensation, potentially assisted by constrained diffusion of DNA [Woldringh, 2002], act in concert to partition the bulk of the nascent chromosomes. However, these processes can neither account for the exquisite directionality of origin movement nor for the distinct temporal and spatial localization patterns observed for the origin regions of multipartite genomes.…”