Essential for magnetosome formation (PubMed:20212111). Can be used to induce magnetosome formation (PubMed:26884433). Part of the probable 18 gene mamAB operon. When both copies of this protein (amb0972 and amb1005) are deleted cells have no magnetic response and no magnetosome membranes. Deletion of just amb0972 leads to an intermediate magnetic response and still makes magnetosome membranes (PubMed:20212111). A careful electron cryotomography exam shows that in the double deletion empty vesicles that might be magnetosome precursors are present (PubMed:26884433). 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. There is an identical gene in the genome (amb1005, AC Q2W8L6). Belongs to the LemA family. Extended N-terminus.