Plasmid replication and partition in Escherichiacoli: is the cell membrane the key?

Abstract

SummaryThe DNA-membrane complex has been the subject of intensive investigation for over 35 years as the possible site for DNA replication in the prokaryotic cell and the site through which newly synthesized chromosomes are segregated into daughter cells. However, the molecular mechanisms which control these phenomena are, for the most part, poorly understood despite genetic, biochemical, and morphologic evidence in favour of their existence. This is probably due to the transient nature and non-covalent interactions that occur between DNA and the membrane. In addition, there is a paucity of knowledge concerning the nature of the membrane receptors for DNA and whether the membrane plays simply a structural or metabolic role in the two processes. Plasmids can provide important insights into the role of the membrane in replication and partitioning because the plasmid life cycle is relatively simple, with replication occurring during the cell cycle and partitioning during cell division. The replicon model of Jacob et al. (1963, Cold Spring Harbor Symp Quant Biol 28: 329-348) still represents a good conceptual framework (with modifications) to explain how plasmid replication and partitioning are linked by the membrane. In its simplest form, the model focuses on specific membrane binding sites (possibly along the equator of the cell) for plasmid (or bacterial) replication, with the membrane acting as a motive force to separate the newly synthesized replicons and their attached sites into daughter cells. Indeed, proteins involved in both plasmid replication and partitioning have been found in membrane fractions and some plasmids require membrane binding for initiation and an active partitioning. We propose that several factors are critical for both plasmid DNA replication and partitioning. One factor is the extent of negative supercoiling (brought about by an interplay of various topoisomerases, but most importantly by DNA gyrase). Supercoiling is known to be critical for initiation of DNA replication but may also be important for the formation of a partition complex in contact with the cell membrane. Another factor is the presence of specific subdomains of the membrane which can interact specifically with origin DNA and possibly other regions involved in partitioning. Such domains may be induced transiently or be present at all times during the cell cycle.

Incompatibility Protein IncC and Global Regulator KorB Interact in Active Partition of Promiscuous Plasmid RK2

“…Because models for partition require an interaction with an as yet unidentified host cell apparatus (3,26,42,89,93), the broad host range of IncP plasmids makes them particularly interesting. Has the IncC-KorB partition system evolved to exploit universal properties of host cell DNA segregation machinery such that it can function in a wide variety of bacterial hosts, or is it specific only for certain hosts?…”

The Active Partition GeneincCof IncP Plasmids Is Required for Stable Maintenance in a Broad Range of Hosts

“…Active partition of bacterial plasmids and chromosomes into newly forming daughter cells is the functional equivalent of mitosis in eukaryotes (10,14,16,19,29). Early studies on plasmid maintenance and plasmid-plasmid incompatibility led to the identification of genetic loci for active partition (2,27,(31)(32)(33).…”

Production of Pcb01, a Plasmid for Dna Immunization Against the Adhesin of Escherichia Coli K88ab

“…In addition DNA gyrase, the enzyme responsible for the formation of negative supercoils, the natural state of almost all plasmids inside their hosts, and a partition complex formed by two other proteins, are required for the stable inheritance of several plasmids. High copy number plasmids can compete with the host for metabolites, resulting in decreased cell viability and the subsequent loss of plasmids (4).…”