There are 3 mitochondrial isoforms of bS18 in mammalia, localizing to 3 distinct sites in the mitoribosome. bS18m (bs18c, this protein) binds to the same site as bacterial bS18, mS40 (bS18b) binds to a novel location of the 28S small subunit, and mL66 (bS18a) binds to the 39S large subunit.