May play a role in magnetite crystal growth and size. Part of the probable 18 gene mamAB operon. Cells have a weak magnetic response and make magnetosome membranes. Magnetite crystals are amorphous, smaller than wild-type and irregularly spaced (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 MamS family.