Jean-Michel Louarn

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In many prokaryotes, asymmetrical mutational or selective pressures have caused compositional skews between complementary strands of replication arms, especially sensitive in the distribution of guanine and cytosine. In Escherichia coli, most of the guanine/cytosine skew is caused by mutation rates differing on leading and lagging strands, but contribution(More)
Escherichia coli FtsK is a multifunctional protein that couples cell division and chromosome segregation. Its N-terminal transmembrane domain (FtsK(N)) is essential for septum formation, whereas its C-terminal domain (FtsK(C)) is required for chromosome dimer resolution by XerCD-dif site-specific recombination. FtsK(C) is an ATP-dependent DNA translocase.(More)
Chromosome dimers in Escherichia coli are resolved at the dif locus by two recombinases, XerC and XerD, and the septum-anchored FtsK protein. Chromosome dimer resolution (CDR) is subject to strong spatiotemporal control: it takes place at the time of cell division, and it requires the dif resolution site to be located at the junction between the two(More)
Escherichia coli FtsK protein couples cell division and chromosome segregation. It is a component of the septum essential for cell division. It also acts during chromosome dimer resolution by XerCD-specific recombination at the dif site, with two distinct activities: DNA translocation oriented by skewed sequence elements and direct activation of Xer(More)
The directions of replication of several prophages integrated with a known orientation in the vicinity of the terminus (tre) of chromosome replication (trp::Mu, min 27; λrev integrated within rac, min 31, man::Mu, min 35), have been established by determining the molecular polarity of Okazaki pieces specific to these prophages. The results obtained strongly(More)
In the dna G t.s. strain BT 308, made lysogenic for the phage λ, nascent DNA was labelled by short pulses of 3H-thymidine, isolated and separated as a function of size by alkaline sucrose gradient sedimentation. The molecular polarity of the labelled DNA was then determined by hybridization to the separated strands of λ DNA. At 30° C, strand r DNA, made in(More)
A strain of Escherichia coli K12 harboring simultaneously the temperature-sensitive dnaA46 mutation and a deletion of the trp-topA-cysB region plates with the same full efficiency at 30° C and 42° C. We have analyzed the possible involvement of the gene coding for topoisomerase I, topA, in this suppression phenomenon. The Ts phenotype was retrieved upon(More)
Strains carrying a dnaA temperature sensitive (t.s.) mutation and a Mu-1 prophage inserted within different genes near the origin of replication have been constructed. For each strain, integratively suppressed Hfrs, named G and D, in which the ori region was replicated clockwise and counterclockwise respectively, were isolated. The strand preferences of(More)
The replication cycle of Escherichia coli dam mutants was analysed and compared with that of isogenic Dam+ strains. Marker frequency analyses indicated no gross difference between the strains. In the Dam− as well as in the Dam+ bacteria, initiation most likely occurs at oriC, replication forks move at a constant and invariant velocity, and termination takes(More)
A λ hybrid phage (λSda1), containing an 8.1 kb EcoRI DNA fragment from the Escherichia coli chromosome, was selected on the basis of its ability to suppress bacterial thermosensitivity caused by the dnaA46 mutation. We have shown that this suppression is due to a recA +-dependent amplification of the 8.1 kb fragment; consistent with this observation,(More)