Selenoprotein M is a selenoprotein, which contains a selenocysteine (Sec) residue at its active site. The selenocysteine M is encoded by the UGA codon that normally signals translation termination. The 3' UTR of selenoprotein genes have a common stem-loop structure, the sec insertion sequence (SECIS), that is necessary for the recognition of UGA as a Sec codon rather than as a stop signal. This gene is expressed in a variety of tissues, and the protein is localized to the perinuclear structures. Selenoprotein M May function as a thiol-disulfide oxidoreductase that participates in disulfide bond formation. This protein is widely expressed and is highly expressed in brain. It is found in Cytoplasm, perinuclear region, Endoplasmic reticulum, Golgi apparatus. Localized to perinuclear structures corresponding to Golgi and endoplasmic reticulum. Experiments results have suggested that selenoprotein M may have an important role in protecting against oxidative damage in the brain and may potentially function in calcium regulation.