Elsevier

Plasmid

Volume 43, Issue 3, May 2000, Pages 200-204
Plasmid

Regular Article
Plasmid R1 Is Present as Clusters in the Cells of Escherichia coli

Communicated by D. Helinski
https://doi.org/10.1006/plas.1999.1457Get rights and content

Abstract

Fluorescence microscopy was used to determine the location(s) of the replication origin of plasmid R1 in exponentially growing cells of Escherichia coli. The number of oriR1 foci per cell was smaller than the number of R1 copies per cell and was found to be the same for a copA mutant of R1 and for the wild-type plasmid. The intensities of individual foci were stronger for the cop mutant than for the wild type. We interpreted these results to imply that the plasmid DNA molecules were localized in small groups/clusters, a result that seems contrary to the earlier observations that plasmid R1 replicates randomly and segregates as a single-copy unit. The implications for the quantitative behavior of plasmid R1 in stability, incompatibility tests, replication, and partition experiments are discussed.

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    The notion of structureless, homogeneous bacterial cytoplasm through which macromolecules diffuse freely to interact by random collisions has been replaced by a system of macromolecular machines designed for specific functions assembled at specific locations at appropriate times such that growth, replication, and cell division processes function in coordination to maintain remarkably error-free cycles of growth and reproduction for generations (1–3). This was also suspected earlier with the discovery of plasmids clustered at characteristic intracellular positions (4, 5) and the sequential movement of the bacterial chromosomes during replication (6–9). Now it has been revealed that the bacterial interior possesses a highly ordered subcellular architecture comprising dynamic networks of cytoskeletal fibers (10–12), multiprotein complexes constituting replication, transcription, and translation machineries assembled at characteristic locations (13–19), and oscillatory relocalization of protein complexes in defined trajectories resulting in concentration gradients (20, 21).

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  • Evaluating quantitative methods for measuring plasmid copy numbers in single cells

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  • Plasmid Segregation: Is a Total Understanding within Reach?

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