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Z-Ring-Associated Proteins Regulate Clustering of the Replication Terminus-Binding Protein ZapT in Caulobacter crescentus.

ABSTRACT: Regulated organization of the chromosome is essential for faithful propagation of genetic information. In the model bacterium Caulobacter crescentus, the replication terminus of the chromosome is spatially arranged in close proximity to the cytokinetic Z-ring during the cell cycle. Although the Z-ring-associated proteins ZapA and ZauP interact with the terminus recognition protein ZapT, the molecular functions of the complex that physically links the terminus and the Z-ring remain obscure. In this study, we found that the physical linkage helps to organize the terminus DNA into a clustered structure. Neither ZapA nor ZauP was required for ZapT binding to the terminus DNA, but clustering of the ZapT-DNA complexes over the Z-ring was severely compromised in cells lacking ZapA or ZauP. Biochemical characterization revealed that ZapT, ZauP, and ZapA interacted directly to form a highly ordered ternary complex. Moreover, multiple ZapT molecules were sequestered by each ZauP oligomer. Investigation of the functional structure of ZapT revealed that the C terminus of ZapT specifically interacted with ZauP and was essential for timely positioning of the Z-ring in vivo Based on these findings, we propose that ZauP-dependent oligomerization of ZapT-DNA complexes plays a distinct role in organizing the replication terminus and the Z-ring. The C termini of ZapT homologs share similar chemical properties, implying a common mechanism for the physical linkage between the terminus and the Z-ring in bacteria.IMPORTANCE Rapidly growing bacteria experience dynamic changes in chromosome architecture during chromosome replication and segregation, reflecting the importance of mechanisms that organize the chromosome globally and locally within a cell to maintain faithful transmission of genetic material across generations. During cell division in the model bacterium Caulobacter crescentus, the replication terminus of the chromosome is physically linked to the cytokinetic Z-ring at midcell. However, the functions of this physical linkage are not fully understood. We adopted biochemical and cell-biological techniques to characterize the linkage, including the terminus-binding protein ZapT and the Z-ring-associated protein ZauP. We obtained evidence that the Z-ring organizes the chromosome terminus into a compact structure at midcell via specific interaction between ZapT and ZauP oligomers. Because these proteins are conserved in diverse Gram-negative bacteria, our findings highlight a novel and conserved role for the linker complex in regulated organization of the chromosome terminus.

SUBMITTER: Ozaki S

PROVIDER: S-EPMC7858052 | biostudies-literature | 2021 Jan

REPOSITORIES: biostudies-literature

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Z-Ring-Associated Proteins Regulate Clustering of the Replication Terminus-Binding Protein ZapT in Caulobacter crescentus.

Ozaki Shogo S Wakasugi Yasutaka Y Katayama Tsutomu T

mBio 20210126 1

Regulated organization of the chromosome is essential for faithful propagation of genetic information. In the model bacterium <i>Caulobacter crescentus</i>, the replication terminus of the chromosome is spatially arranged in close proximity to the cytokinetic Z-ring during the cell cycle. Although the Z-ring-associated proteins ZapA and ZauP interact with the terminus recognition protein ZapT, the molecular functions of the complex that physically links the terminus and the Z-ring remain obscure ...[more]

PMID: 33500340

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Project description:Cell division requires proper spatial coordination with the chromosome, which undergoes dynamic changes during chromosome replication and segregation. FtsZ is a bacterial cytoskeletal protein that assembles into the Z-ring, providing a platform to build the cell division apparatus. In the model bacterium Caulobacter crescentus, the cellular localization of the Z-ring is controlled during the cell cycle in a chromosome replication-coupled manner. Although dynamic localization of the Z-ring at midcell is driven primarily by the replication origin-associated FtsZ inhibitor MipZ, the mechanism ensuring accurate positioning of the Z-ring remains unclear. In this study, we showed that the Z-ring colocalizes with the replication terminus region, located opposite the origin, throughout most of the C. crescentus cell cycle. Spatial organization of the two is mediated by ZapT, a previously uncharacterized protein that interacts with the terminus region and associates with ZapA and ZauP, both of which are part of the incipient division apparatus. While the Z-ring and the terminus region coincided with the presence of ZapT, colocalization of the two was perturbed in cells lacking zapT, which is accompanied by delayed midcellular positioning of the Z-ring. Moreover, cells overexpressing ZapT showed compromised positioning of the Z-ring and MipZ. These findings underscore the important role of ZapT in controlling cell division processes. We propose that ZapT acts as a molecular bridge that physically links the terminus region to the Z-ring, thereby ensuring accurate site selection for the Z-ring. Because ZapT is conserved in proteobacteria, these findings may define a general mechanism coordinating cell division with chromosome organization.IMPORTANCE Growing bacteria require careful tuning of cell division processes with dynamic organization of replicating chromosomes. In enteric bacteria, ZapA associates with the cytoskeletal Z-ring and establishes a physical linkage to the chromosomal replication terminus through its interaction with ZapB-MatP-DNA complexes. However, because ZapB and MatP are found only in enteric bacteria, it remains unclear how the Z-ring and the terminus are coordinated in the vast majority of bacteria. Here, we provide evidence that a novel conserved protein, termed ZapT, mediates colocalization of the Z-ring with the terminus in Caulobacter crescentus, a model organism that is phylogenetically distant from enteric bacteria. Given that ZapT facilitates cell division processes in C. crescentus, this study highlights the universal importance of the physical linkage between the Z-ring and the terminus in maintaining cell integrity.

Dataset Information

Z-Ring-Associated Proteins Regulate Clustering of the Replication Terminus-Binding Protein ZapT in Caulobacter crescentus.

Publications

Z-Ring-Associated Proteins Regulate Clustering of the Replication Terminus-Binding Protein ZapT in Caulobacter crescentus.

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