Eukaryotic molybdoenzymes use a unique molybdenum cofactor (MoCo) consisting of a pterin, termed molybdopterin, and the catalytically active metal molybdenum. MoCo is synthesized from precursor Z by the heterodimeric enzyme molybdopterin synthase. The large and small subunits of molybdopterin synthase are both encoded from this gene by overlapping open reading frames. The proteins were initially thought to be encoded from a bicistronic transcript. They are now thought to be encoded from monocistronic transcripts. Alternatively spliced transcripts have been found for this locus that encode the large and small subunits.