The incorporation of selenocysteine during translation. A serine-charged tRNA (SelC) with the anticodon 5′-UCA recognizes a UGA stop codon. The Ser-tRNA^Sec is enzymatically converted to selenocysteyl-tRNA^Sec (Sec-tRNA^Sec) by the protein SelA, which uses selenophosphate and releases P_i on attachment of the selenium to the amino acid. SelB is an elongation factor that recognizes a specific hairpin in the mRNA and also binds Ser-tRNA^Sec, facilitating incorporation of selenocysteine into the protein.