A complementary DNA clone was screened with a single-copy genomic DNA fragment derived from yeast artificial chromosome (YAC) clone D142H8 which contained phosphoribosylglycinamide formyltransferase (GART) gene and an accessory factor-1 (AF-1) gene of human interferon receptor-gamma receptor. The length of the clone is 1337 nt and has an the longest open reading frame (ORF) of 349 amino acids. Genbank search revealed that it is the forth member of quinone oxidoreductase super family. Therefore, the gene was named as quinone oxidoreductase family-4 (qorf-4). The putative protein contains the conserved glycine-rich NADPH binding motif (A/GXGXXGXXXA), which suggest that it might have an enzymatic activity, possibly reductase with NADPH as a cofactor. Multiple tissue Northern blot data showed that the mRNA was expressed ubiquitously. The gene of qorf-4 is located on human chromosome 21q22.1 region where the YAC was mapped. The location of the gene is further localized on the YAC D142H8 with respect to 2 NotI sites and GART and AF-1 loci.