ANALYSES OF THE CDNA CLONES FOR BETA 1-4 GALACTOSYLTRASFERASE

需要一种特定的糖基转移酶来合成 糖蛋白和糖脂的低聚糖部分，它们 被称为糖共轭化合物。半乳糖基转移酶(GAL- Transf)是转移酶的一个亚群，构成了一个家族 将半乳糖从UDP-GAL转移到非 不同糖结合物的低聚糖还原残留量 以及单糖。我们已经启动了分子 了解半乳糖转运蛋白调控的克隆方法 活性，对于产生特定的细胞表面抗原是必不可少的 决定因素。在我们以前对基因结构的研究中 半乳糖转运蛋白修饰蛋白α-乳清蛋白的分析 我们证明了与α-乳白蛋白相互作用的结构域 使用GAL-Transf完全由一个单独的外显子编码。我们有 牛GlcNAc 1-4编码基因的克隆和序列分析 Gal-Transf.几个序列相关的cDNA克隆的分析 结果表明：1)1)至少有两条染色体序列 4)Gal-Transf；2)有两类主要的mRNAs 共享编码蛋白质的共同核苷酸序列 120个残基的相同的羧基末端和共享相同的3‘ 非编码序列。一类编码1-4个GAL-Transf的克隆 蛋白质序列；3)该酶必须合成为 原蛋白，并以切割产物的形式分泌 具有酶活性；4)存在于 利用基因序列来产生不同大小mRNAs 它们在3‘非编码区的长度不同；5) 在5‘端有不同核苷酸序列的克隆 与编码1-4个GAL-Transf的克隆相比，不要 编码三个开放读数中的任何一个蛋白质序列 这些框架表明它们可能代表未剪接的前体 6)几个相关基因的核苷酸序列分析 CDNA克隆表明，一种复杂的替代处理 前体mRNA产生半乳糖转运蛋白mRNAs。

A specific glycosyltransferase is required for the synthesis of oligosaccharide moieties of glycoproteins and glycolipids, which are referred to as glycoconjugates. Galactsyltransferases (gal- transf), a subgroup of the transferases, constitute a family of enzymes which transfer galatose from UDP-gal to the non- reducing residues of oligosaccharides of various glycoconjugates as well as to monosaccharides. We have initiated the molecular cloning approach to understand the modulation of the gal-transf activity, essential for generating specific cell-surface antigenic determinants. In our previous studies on the gene structural analyses of alpha-lactalbumin, a modifier protein of gal-transf, we showed that the domain of alpha-lactalbumin that interacts with gal-transf is coded entirely by a separate exon. We have now cloned and sequenced cDNA coding for bovine GlcNAc 1-4 gal-transf. Analysis of several sequence-related cDNA clones showed: 1) There are at least two chromosomal sequences for 1- 4 gal-transf; 2) There are two major classes of mRNAs which share common nucleotide sequences encoding the proteins with the same carboxy-terminal end of 120 residues and share same 3' noncoding sequence. One class of clones encode 1-4 gal-transf protein sequence; 3) The enzyme must be synthesized as a proprotein and secreted as cleaved product which is enzymatically active; 4) Series of poly(A) sites present in the gene sequence are utilized to generate mRNAs of different sizes which vary in length at the 3' non-coding region; 5) The cDNA clones which have different nucleotide sequence at the 5' end compared to the clones coding for the 1-4 gal-transf, do not encode any protein sequence in any of the three open reading frames suggesting that they may represent unspliced precursor mRNAs; 6) The nucleotide sequence analysis of several related cDNA clones suggest that a complex alternative processing of the precursor mRNA occurs to generate gal-transf mRNAs.