SEPHS1 (Selenophosphate Synthetase 1) is a gene that encodes an enzyme essential for the biosynthesis of selenoproteins, which contain the amino acid selenocysteine. Mainly found in the cytoplasm, SEPHS1 plays a crucial role in selenium metabolism by producing selenophosphate, the activated form of selenium needed for incorporating selenocysteine into proteins. Through this function, SEPHS1 ensures the proper synthesis of selenoproteins, which are vital for various cellular processes and overall cell health.