ANALYSES OF THE CDNA CLONES FOR BETA 1-4 GALACTOSYLTRASFERASE

一种特殊的糖基转移酶是合成 糖蛋白和糖脂的寡糖部分， 称为糖缀合物。 半乳糖基转移酶（gal- transf），转移酶的一个亚组，构成了一个家族， 将半乳糖从UDP-半乳糖转移到非半乳糖的酶， 各种糖缀合物的寡糖的还原残基 以及单糖。 我们已经启动了 克隆方法来了解gal-transf的调节 产生特异性细胞表面抗原所必需的活性 决定因素 在我们以前对基因结构的研究中， 对α-乳白蛋白，一种Gal-transf的修饰蛋白， 我们发现α-乳白蛋白的结构域 与gal-transf完全由单独的外显子编码。 我们有 现已克隆并测序了编码牛GlcNAc 1-4的cDNA 几个序列相关cDNA克隆的gal-transf分析 结果表明：1）1- 3号染色体至少有两条染色体序列， 4 gal-transf; 2）有两种主要类型的mRNA， 共享编码蛋白质的共同核苷酸序列， 相同的120个残基的羧基末端和共享相同的3' 非编码序列 一类克隆编码1- 4gal-transf 蛋白质序列; 3）酶必须合成为 前蛋白并作为切割产物分泌， 酶活性; 4）存在于所述酶中的一系列多聚（A）位点， 基因序列用于产生不同大小的mRNA 其在3'非编码区的长度不同; 5）cDNA 在5 ′端具有不同核苷酸序列的克隆 与编码1- 4Gal-transf的克隆相比， 编码三个开放阅读中任何一个的任何蛋白质序列 提示它们可能代表未剪接的前体 6）对几种相关基因的核苷酸序列进行分析 cDNA克隆表明，一个复杂的替代加工， 前体mRNA产生gal-transf mRNA。

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.