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. Genes encoding selenocysteine contain a stem-loop secondary structure in their 3' UTR called a selenocysteine insertion sequence (SECIS) element. The protein encoded by this gene contains a selenocysteine residue in its predicted active site. There is a pseudogene for this gene on chromosome 5. [provided by RefSeq, Aug 2013].