Essential for magnetosome formation (PubMed:20212111). May bind magnetite (Probable). May be involved in an early stage of magnetosome nucleation (By similarity). Tagged protein forms straight lines extending along most of the cell associated with its inner curvature, in the correct position to be associated with magnetosomes (PubMed:20212111, PubMed:21414040, PubMed:21883528, PubMed:28790202). In a mamK deletion MamI forms a linear punctate pattern, suggesting it is associated with magnetosomes (PubMed:20212111). In a mamE deletion MamI forms a linear punctate pattern (PubMed:21414040). In double mamJ/limJ deletion MamI forms a linear punctate pattern (PubMed:21883528). Part of the probable 18 gene mamAB operon. Cells have no magnetic response and no magnetosome membranes (PubMed:20212111). Deletion of genes mamH to mamV (amb0961 to amb0978) gives cells with no magnetosomes and no magnetic response (PubMed:20212111). A short loop (residues 21-31, which is probably in the magnetosome lumen) when inserted into a Salmonella flagellin protein (FliC) binds magnetite, which may be used to purify particular forms of magnetite. 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 MamI protein family.