This gene encodes an enzyme that synthesizes selenophosphate from selenide and ATP. Selenophosphate is the selenium donor used to synthesize selenocysteine, which is co-translationally incorporated into selenoproteins at in-frame UGA codons. This protein itself contains a selenocysteine residue in its predicted active site. The 3' UTR of the gene has a stem-loop secondary structure called a selenocysteine insertion sequence (SECIS) element, which allows UGA to direct the incorporation of selenocysteine rather than signal a translational stop. Alternatively spliced transcripts have been identified, but their biological validity has not been determined. [provided by RefSeq]