Murine α-N-acetylgalactosaminidase: Isolation and expression of a full- length cDNA and genomic organization: Further evidence of an α-galactosidase gene family

Recent characterization of the human sequences encoding two lysosomal hydrolases, α-galactosidase A (α-Gal A) and α-N-acetylgalactosaminidase (αGalNAc) revealed that these two enzymes with distinct enzymatic activities shared about 50% overall amino acid identity and that their genomic sequences had a conserved common gene structure. These findings suggested that these genes, which are located on different chromosomes, arose by duplication and divergence from a common ancestral gene. To further compare this α- galactosidase gene family, the murine α-GalNAc cDNA and genomic sequences were isolated and characterized. The full-length cDNA contained an open- reading frame of 1245 bp encoding a 415 amino acid polypeptide and had 5' and 3' untranslated regions of 94 and 333 bp, respectively. The coding region had 81% nucleotide and 81.9% amino acid identities with those of the corresponding human α-GalNAc sequence. Northern analysis revealed a single transcript of ~1.9 kb. The functional integrity of the cDNA was demonstrated by transient expression in COS-1 cells. The murine α-GalNAc genomic sequence spanned ~9 kb and was identical in structure with the human α-GalNAc gene with eight introns interrupting the coding sequence at identical positions. In addition, the deduced amino acid sequence of the murine α-GalNAc gene was highly homologous with α-GalNAc and α-Gal A genes from other species providing further support for a common evolutionary ancestor of the α- galactosidase gene family. The availability of the murine gene will permit additional evolutionary comparisons, structure/function analyses, and the generation of mice with α-GalNAc deficiency by gene targeting.