Proia R L, Soravia E
J Biol Chem. 1987 Apr 25;262(12):5677-81.
The lysosomal enzyme, beta-hexosaminidase, is composed of two chains, alpha and beta. In Tay-Sachs disease, mutations in the gene encoding the alpha-chain produce a beta-hexosaminidase deficiency that results in the storage of its natural substrate, GM2 ganglioside. To obtain the background information for the eventual identification of the mutational errors in Tay-Sachs disease and to determine possible relationships between protein and gene structure, we have characterized the intron-exon organization of the human beta-hexosaminidase alpha-chain gene. Several overlapping clones were isolated from human genomic libraries constructed in cosmid and bacteriophage vectors. The cloned genomic DNA was analyzed by restriction endonuclease mapping, Southern blotting, and DNA sequencing. It was determined that the alpha-chain gene is approximately 35 kilobases long and is split into 14 exons. Sequences which resemble the "TATA" and "CAAT" transcriptional regulatory motifs are present at the 5' end of the gene. Differential transcription or processing of the most 3' exon of the gene results in two alpha-chain mRNAs with different 3'-untranslated regions. The first exon of the gene encodes the amino-terminal portion of the alpha-chain which is removed during the proteolytic maturation of the enzyme, raising the possibility that this segment may exist as a functional domain.
溶酶体酶β-己糖胺酶由α和β两条链组成。在泰-萨克斯病中，编码α链的基因突变会导致β-己糖胺酶缺乏，进而致使其天然底物GM2神经节苷脂蓄积。为获取最终鉴定泰-萨克斯病突变错误的背景信息，并确定蛋白质与基因结构之间的可能关系，我们已对人β-己糖胺酶α链基因的内含子-外显子组织进行了表征。从以黏粒和噬菌体载体构建的人基因组文库中分离出了几个重叠克隆。通过限制性内切酶图谱分析、Southern印迹分析和DNA测序对克隆的基因组DNA进行了分析。确定α链基因约35千碱基长，被分割为14个外显子。基因5′端存在类似于“TATA”和“CAAT”转录调控基序的序列。该基因最3′端外显子的差异转录或加工产生了两种具有不同3′非翻译区的α链mRNA。该基因的第一个外显子编码α链的氨基末端部分，该部分在酶的蛋白水解成熟过程中被去除，这增加了该片段可能作为功能域存在的可能性。
