A role for division-site-selection protein MinD in regulation of internucleoid jumping of Soj (ParA) protein in Bacillus subtilis

The Bacillus subtilis soj-spoOJ locus encodes two proteins belonging to a family of proteins (the ParAB proteins) with dual roles in plasmid or chromosome segregation and transcriptional regulation. Soj protein was previously shown to be capable of abrupt subcellular relocation. The movement was highly cooperative and at any moment, most of the Soj in any cell formed a single large 'patch' covering all or part of one nucleoid. Movement, and co-operativity, in the sense of formation of a single patch, was dependent on SpoOJ. Movement, but not co-operativity, was also shown to be dependent, directly or indirectly, on FtsZ protein. We now report that the ftsZ effect arises because jumping onto a nucleoid is promoted by proximity to a cell pole. Studies of other mutants affected in cell division suggest that the attraction to the cell pole is mediated by the division-site-selection protein, MinD (which localizes at the cell poles). It does not require MinC, the main effector of the division site selection system. A mutant form of Soj, putatively locked in the ATP form of the protein, interacts with the cell pole (dependent on MinD) but not with the nucleoid. These results identify a novel function for MinD and demonstrate an intriguing link between proteins involved in the cell division and chromosome segregation machineries.