Isolation and characterization of the DLAD/Dlad genes, which lie head-to-head with the genes for urate oxidase

We previously found that a novel DNA endonuclease named DLAD (DNase II-Like Acid DNase) is specifically expressed in murine liver. Here, we describe t he isolation and characterization of the human DLAD and mouse Mad genes. Bo th DLAD and Mad consist of 6 exons. DLAD encodes a 361 amino acid protein s haring 34.6% amino acid identity with human DNase II. Although a recombinan t protein for the putative human DLAD has a divalent cation-independent aci d DNase activity, expression of the MAD mRNA containing the entire open rea ding frame was not detected in any human tissues tested, except for lung, i n which a short 1.1 kb transcript lacking the first two exons is expressed. Interestingly, sequence analysis of Mad showed that the 1st exon of the ur ate oxidase gene, Uox, is located on the opposite strand in its 5'-flanking region. The head-to-head organization of DLAD and UOX is conserved in the human genomic sequence. Promoter analysis revealed that the intergenic regi on between Mad and Uox has promoter activity for both the Mad and Uox direc tions, however, the corresponding human genomic fragment has promoter activ ity only for DLAD. It is known that murine Uox is expressed only in the liv er, whereas human UOX has been inactivated as a pseudogene. On the basis of these results, the expression of DLAD/Dlad and UOX/Uox is suggested to be coordinated by a common regulatory mechanism(s), and the balance between th e two enzymes is thought to be important for maintaining the purine nucleot ide pool in the liver. (C) 2001 Academic Press.