Selenocysteine insertion sequence-binding protein 2 (SECISBP2) is required for the incorporation of the amino acid selenocysteine (Sec) into proteins during translation. The mRNA triplet UGA is usually a stop codon, but the presence of a Sec insertion sequence element (SECIS) in the 3'-untranslated region of an mRNA, and its binding to SECISBP2, leads to insertion of Sec into the protein instead. Mutations in the SECISBP2 gene that alter the amino acid sequence or cause splicing defects lead to abnormal thyroid hormone metabolism. A splice variant of SECISBP2 is localized to the mitochondrion rather than the nucleus [].This entry also includes selenocysteine insertion sequence-binding protein 2-like (SECISBP2L), which also binds SECIS, but in mammals does not lead to incorporation of Sec into proteins, because it lacks the SECIS dependent domain association that is found in SECISBP2. An invertebrate orthologue is fully competent for Sec incorporation, however [].Homologues are also known from bacteria.
