Essential for magnetosome formation. May associate transiently with magnetosomes; in about 10% of cells, GFP tagged protein is aligned in dots or very short filaments similar to magnetosome distribution. 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). 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 MamL family.