The min locus, which confers topological specificity to cell division, is not involved in its coupling with nucleoid separation

MinCD proteins control the septation process during sporulation of Bacillus subtilis

Mutation of the divIVB locus in Bacillus subtilis causes misplacement of the septum during cell division and allows the formation of anucleate minicells. The divIVB locus contains five open reading frames (ORFs). The last two ORFs (minCD) are homologous to minC and minD of Escherichia coli but a minE homolog is lacking in B. subtilis. There is some similarity between minicell formation and the asymmetric septation that normally occurs during sporulation in terms of polar septum localization. However, it has been proposed that MinCD has no essential role in sporulation septum formation. We have used electron microscopic studies to show septation events during sporulation in some minD strains. We have observed an unusually thin septum at the midcell position in minD and also in minD spoIIE71 mutant cells. Fluorescence microscopy also localized a SpoIIE-green fluorescent protein fusion protein at the midcell site in minD cells. We propose that the MinCD complex plays an important role in asymmetric septum formation during sporulation of B. subtilis cells.

Linkage map of Escherichia coli K-12, edition 10: the traditional map

This map is an update of the edition 9 map by Berlyn et al. (M. K. B. Berlyn, K. B. Low, and K. E. Rudd, p. 1715-1902, in F. C. Neidhardt et al., ed., Escherichia coli and Salmonella: cellular and molecular biology, 2nd ed., vol. 2, 1996). It uses coordinates established by the completed sequence, expressed as 100 minutes for the entire circular map, and adds new genes discovered and established since 1996 and eliminates those shown to correspond to other known genes. The latter are included as synonyms. An alphabetical list of genes showing map location, synonyms, the protein or RNA product of the gene, phenotypes of mutants, and reference citations is provided. In addition to genes known to correspond to gene sequences, other genes, often older, that are described by phenotype and older mapping techniques and that have not been correlated with sequences are included.

Partition of P1 plasmids in Escherichia coli mukB chromosomal partition mutants

The partition system of the low-copy-number plasmid/prophage of bacteriophage P1 encodes two proteins, ParA and ParB, and contains a DNA site called parS. ParB and the Escherichia coli protein IHF bind to parS to form the partition complex, in which parS is wrapped around ParB and IHF in a precise three-dimensional conformation. Partition can be thought of as a positioning reaction; the plasmid-encoded components ensure that at least one copy of the plasmid is positioned within each new daughter cell. We have used an E. coli chromosomal partition mutant to test whether this positioning is mediated by direct plasmid-chromosomal attachment, for example, by pairing of the partition complex that forms at parS with a bacterial attachment site. The E. coli MukB protein is required for proper chromosomal positioning, so that mukB mutants generate some cells without chromosomes (anucleate cells) at each cell division. We analyzed the plasmid distribution in nucleate and anucleate mukB cells. We found that P1 plasmids are stable in mukB mutants and that they partition into both nucleate and anucleate cells. This indicates that the P1 partition complex is not used to pair plasmids with the host chromosome and that P1 plasmids must be responsible for their own proper cellular localization, presumably through host-plasmid protein-protein interactions.

FtsZ and nucleoid segregation during outgrowth of Bacillus subtilis spores

Spores of a strain of Bacillus subtilis in which ftsZ was under the control of the spac promoter were allowed to germinate and grow out in the presence of increasing concentrations of isopropyl-beta-D-thiogalactopyranoside (IPTG). Over the IPTG concentration range of 0 to 10(-3) M, the level of FtsZ from the time when the first nucleoid segregations were occurring, measured in Western blot (immunoblot) transfer experiments, varied between 15 and 100% of that in the wild type. Septation was completely blocked (for at least several hours) when the amount of FtsZ was < 30% of the wild-type level. At all levels of ftsZ induction, the timing and rate of segregation of nucleoids following the first round of replication were unaltered. It is concluded that FtsZ has no direct role in nucleoid segregation in this situation.