Required for correct biomineralization of the magnetosome; probably transports some form of iron. Partially functionally redundant with MamZ. Tagged protein forms straight lines with a punctate pattern extending along most of the cell associated with its inner curvature, in the correct position to be associated with magnetosomes, but longer than the usual chain. First gene of the probable 18 gene mamAB operon. No visible phenotype, magnetic response is slightly reduced and magnetosome membrane formation is wild-type (PubMed:20212111). 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 major facilitator superfamily.