The incorporation of
selenocysteine into a protein requires the concerted action of an mRNA element called a sec insertion sequence (
SECIS), a selenocysteine-specific translation elongation factor and a SECIS binding protein. With these elements in place, a UGA codon can be decoded as selenocysteine. SBP2 is a nuclear protein that functions as a SECIS binding protein, but experimental evidence indicates that SBP2 is cytoplasmic. == Clinical significance ==