In mitochondria, S-adenosylmethionine-dependent methyltransferase chaperone that supports both coenzyme Q biosynthesis, by stabilizing its components, such as COQ5, and NADH:ubiquinone oxidoreductase complex (complex I, MT-ND1) assembly, by stabilizing complex I assembly factors, such as NDUFAF5. . This is the function of Ensembl gene identifier ENSG00000145337 (PYURF, PIGY upstream open reading frame).