Impairment of cell division in tolA mutants of Escherichia coli at low and high medium osmolarities.

Mutations in the tolA gene of Escherichia coli cause the cell to become sensitive to detergents and to some antibiotics, to release periplasmic enzymes and to be resistant to group A colicins; tolA mutations also lead to mucoid phenotype. TolA is a three-domain protein anchored in the inner membrane by its N-terminal domain. The second domain is proposed to span the periplasmic space and to interact with trimeric porins of the outer membrane.

Increased expression of a hemimethylated oriC binding protein, SeqA, in an aphA mutant.

In Escherichia coli, the origin of DNA replication, oriC, becomes transiently hemimethylated at the GATC sequences immediately after initiation of replication and this hemimethylated state is prolonged because of its sequestration by a fraction of outer membrane. This sequestration is dependent on a hemimethylated oriC binding protein such as SeqA. We previously isolated a clone of phage lambda gt11 called hobH, producing a LacZ fusion protein which recognizes hemimethylated oriC DNA.

Co-ordination between membrane oriC sequestration factors and a chromosome partitioning protein, TolC (MukA).

oriC DNA in the hemimethylated (but not in the fully methylated) state reacts with an Escherichia coli K-12 outer membrane preparation. This reaction is drastically reduced when the membrane preparation of a seqA null mutant is used. An in vitro reconstitution of the activity was undertaken by adding a partially purified SeqA protein to a seqA mutant membrane without success.

Importance of the replication origin sequestration in cell division of Escherichia coli.

The DNA adenine methyltransferase of Escherichia coli methylates adenines at GATC sequences. The mutant deficient in this methylase has no apparent deficiency in the cell division process in spite of the absence of both synchrony in initiations of chromosomal DNA replication and sequestration of replication origin (oriC) at hemimethylated state. However, the dam mutant cannot resume cell division after hyperosmotic shock differing from the wild-type strain.

Immediate and transient inhibition of the respiration of Escherichia coli under hyperosmotic shock.

The respiration of Escherichia coli is severely inhibited, during hyperosmotic stress period, as a consequence of plasmolysis; deplasmolysis allows the cell to recover respiration. A mutant lacking all K+ transport systems can neither deplasmolyze nor recover respiration unless betaine is present in the medium. Betaine, in these conditions, increases both cytoplasmic volume and respiration; this suggests a control of respiration by cytoplasmic volume.