The process by which Bacillus subtilis changes from vegetative growth into a distinct developmental pathway that results in spore formation has been studied extensively (5, 9). A key event in the initial stages of spore development is the movement of the two chromosomes away from the cell center and their eventual attachment to the cell poles (axial filament formation). This occurs in two distinct steps, beginning with the extraction of the chromosomal origin from its vegetative position and movement towards the cell pole (18). In a second step, the chromosome is decorated with the DNA binding protein RacA and is attached to the cell pole (1, 17). Interestingly, both of these events require the vegetative cell division positioning protein DivIVA (2, 4). DivIVA is a small, predominantly coiled-coil protein that is recruited to the vegetative cell division site after the assembly of FtsZ (12) and the incorporation of FtsW (data not shown). DivIVA remains associated with the division site as it matures and eventually splits to form the two new cell poles (4). The subcellular localization of DivIVA is crucial for the correct distribution of a bipartite cell division inhibitor complex consisting of the MinC and MinD proteins (MinCD) (12). By maintaining MinCD at the cell pole, DivIVA prevents the assembly of an FtsZ ring in the chromosome free space at the cell pole and promotes vegetative division at the midcell. Recently we identified a polar targeting mutant of DivIVA that functions in both vegetative growth and sporulation (14). DivIVAR18C localizes to the chromosome in the presence of Spo0J/Soj and can be observed to occur transiently at the cell division site. It appears that the temporary association of this mutant protein with the division site is sufficient to partially localize MinCD. More intriguingly, the association of the mutant protein with the chromosome is sufficient to allow the relocation of the chromosome by MinD and Spo0J/Soj at the onset of sporulation. To identify proteins in proximity to DivIVA and DivIVAR18C, we have developed a coimmunoprecipitation (co-IP) protocol for the isolation of myc-DivIVA-containing complexes.