Regulates the dynamic behavior of MamK filaments; paralog LimJ also promotes MamK turnover. At least one other protein besides MamJ and LimJ is required for MamK turnover (PubMed:21883528). May connect magnetosomes to MamK filaments (Probable). Moves from the cell poles towards midcell; movement does not depend on the treadmilling ability of MamK, suggesting MamJ associates and disassociates continuously from the MamK filament (By similarity). Forms homooligomers. Interacts with MamK. Tagged protein extends in a line from one pole to the other, and is longer than the magnetosome chain. Part of the probable 18 gene mamAB operon. The center of the protein encodes 8.6 repetitions of a Glu-rich sequence. Single gene deletion, no effect on magnetic response or MamK filaments, gaps form in the magnetosome chain. A double mamJ/limJ deletion has wild-type magnetic response, but forms large gaps in the magnetosome chains reminiscent of the mamK deletion. MamK forms bundles in these gaps, but the MamK filaments are no longer dynamic (PubMed:21883528). Deletion of genes mamH to mamV (amb0961 to amb0978) gives cells with no magnetosomes and no magnetic response (PubMed:20212111). This bacteria makes up to 20 cubo-octahedral magnetosomes of about 45 nm in diameter which contain membrane-bound crystals of magnetite (Fe(3)O(4)). Expression of just the minimal mamAB gene cluster (amb0961 to amb0978), including this gene, is sufficient to form a minimal magnetosome chain with small magnetite particles. Belongs to the magnetosome MamJ protein family.