Figure 1.

DNA traffic in bacteria. (A) Coordination between chromosome segregation and cell division in B. subtilis and E. coli. (i) Normal vegetative cell division in E. coli or B. subtilis. When the bulk of the sister chromosomes remains at mid-cell, nucleoid occlusion factors prevent FtsZ-ring formation. Segregation of the nucleoids away from mid-cell allows the recruitment of the division machinery. (ii) Sporulation in B. subtilis. Only a third of the chromosome is trapped in the prespore compartment during the asymmetric cell division of sporulation. SpoIIIE transports the remaining two-third of the chromosome. (iii) Chromosome dimer resolution in E. coli. RecA-mediated homologous recombination during replication can lead to the formation of dimers of the circular chromosome. Replication and segregation proceed until the bulk of the sister chromosomes are distributed in each daughter cell, but the two nucleoids remain linked by DNA passing through the division septum. FtsK-dependent DNA transport brings dif sites together. FtsK subsequently activates Xer recombination to resolve the dimer into monomers. (B) Schematic representation of FtsK, SpoIIIE and the Tra proteins of two Streptomycetes conjugative plasmids. Transmembrane domains are depicted as vertical black bars and translocation modules as blue rectangles. Numbers indicate the position of amino acid residues. A grey rectangle indicates the part of FtsK_N that belongs to a ∼50 amino acid region (FtsK₅₀; aa 179–230) that increases the efficiency with which FtsK peptides carrying an intact C-terminal domain activate Xer recombination under low expression levels.