| Popis: |
Coordinating chromosome duplication and segregation with cell division is clearly critical for bacterial species. This precise choreography required is even more complex in species with more than one chromosome. The alpha subgroup of bacteria contains not only one of the best studied bacterial species, Caulobacter crescentus but also several species with more than one chromosome. Rhodobacter sphaeroides is an alpha proteobacterium with two chromosomes, but, unlike C. crescentus it divides symmetrically rather than buds and lacks the complex CtrA dependent control mechanism. By following the Ori and Ter regions of both chromosomes and associated ParA and ParB proteins relative to the cell division proteins FtsZ and MipZ we have identified a different pattern of chromosome segregation and cell division. The pattern of chromosome duplication and segregation resembles Vibrio cholerae not Agrobacterium tumerfaceans with duplication of the origin and terminus regions of chromosome 2 controlled by chromosome 1. Key proteins are localised to different sites when compared to C. crescentus. OriC1 and ParB1 is localised to the old pole while MipZ and FtsZ localise to the new pole. Movement of ParB1 to the new pole following chromosome duplication releases FtsZ which forms a ring at midcell, but, unlike reports for other species, MipZ monomers go not form a gradient but oscillate between poles with the nucleotide bound monomer and the dimer localising to midcell. MipZ dimers form a single ring, with a smaller diameter, close to the FtsZ ring at midcell and constricts with the FtsZ ring. Overproduction of the dimer form results in filamentation, suggesting MipZ dimers are regulating FtsZ activity and thus septation. This is an unexpected role for MipZ and provides a new model for the integration of chromosome segregation and cell division. |
