MOLECULAR-CLONING AND CHROMOSOMAL LOCALIZATION OF A HUMAN GENE ENCODING D-AMINO-ACID OXIDASE

Genomic clones covering the entire sequence of the gene encoding human D-amino-acid oxidase (DAO) (EC 1.4.3.3), one of the principal and characteristic flavoenzymes of peroxisomes, were isolated from human placental genomic libraries with the aid of a previously cloned cDNA for human DAO as a probe. Nucleotide sequence analysis revealed that the gene, present as a single copy in the human genome, comprises 11 exons and spans 20 kilobase pairs. The protein sequences containing the catalytically important residues, Tyr-228 and His-307, are coded for by separate exons. Heterologous transcription initiation sites were identified by primer extension analysis, and the sequence of the 5'-flanking region of the DAO gene was found to show some features common to other mammalian genes, such as those of glucocorticoid and the cAMP-responsive element. An additional noteworthy feature is the presence of promoter-like sequences in the first intron of the gene. In addition, two sequences of alternating pyrimidine and purine nucleotides, (CA)20 and (CA)17, are also present in the first intron. Such sequences may play some role in the expression of the DAO gene in human tissues. With the use of genomic DNAs prepared from human and Chinese hamster somatic hybrid cells as templates for the polymerase chain reaction, the gene for DAO was localized to human chromosome 12.