GENETIC ANALYSIS OF MEMBRANE IMMUNOGLOBULIN

膜免疫球蛋白M(IgM)是发育信号的受体 刺激小B淋巴细胞分化为免疫球蛋白M分泌 浆细胞。膜免疫球蛋白糖蛋白的结构研究进展 B淋巴细胞肿瘤与分泌型IgM的测定及比较 来自近亲交配的小鼠。这两种形式除了它们的羧基外都是相同的 终极迷你。膜形式具有用于膜的疏水“尾巴” 相互作用，可分泌的形式有一个亲水的“尾巴”，允许 它形成多聚体并被分泌。一个基因编码常量 Mu区；不同的基因片段编码替代的羧基 终极迷你。据认为，这两种形式的亩是由 单个初级转录本的RNA选择性剪接。我们已经使用了 同时表达膜(MIgM)和分泌型(SIGM)的小鼠肿瘤细胞 表格。从这些细胞中，我们免疫选择了50多个变种 不再表达mIgM。其中14个已经被广泛地 以速率、量、稳定性和糖基化为特征的 MU和MUS蛋白及其编码MU和MUS的mRNA的量和比率 Mus.一种变异体遭受了12号染色体部分的大量缺失 因此，只合成了启动于 未重排同源基因的J-CMU内含子。所有其他变种都有 南方斑点上与野生型完全相同的图案。两个变种 已经确定了改变蛋白质的基因，但每一种都会影响两种基因 妈妈和妈妈。三个变异体显示没有检测到MU蛋白合成 而且只有“不育”的细胞质MU转录本。然而，他们的比率 Mu基因的转录水平仅略低于野生型。分析了几个问题 这些变异体的RNA加工、DNA序列测定和新变异体的选育 具有特定表型的变种目前正在进行中。 我们已经开始在体外产生克隆的Mu基因的特异性突变。 膜Mu的两个膜特异性基因片段已经融合。 与编码A细胞外部分的基因片段一起 “报告蛋白”(小鼠主要组织相容性复合体类的一部分 I基因)。这种结构被重新引入培养的细胞中，以 监测其作为膜蛋白的行为。它将进一步修改为 确定分子中对膜表达至关重要的区域。(CS)

Membrane immunoglobulin M (IgM) is the receptor for a developmental signal that stimulates a small B lymphocyte to differentiate into an IgM secreting plasma cell. The structure of the membrane IgM glycoprotein has recently been determined and compared with secreted IgM by using B-lymphocyte tumors from inbred mice. These two forms are identical except for their carboxy termini. The membrane form has a hydrophobic "tail" for membrane interaction, and the secretable form has a hydrophilic "tail" that allows it to form multimers and to be secreted. One gene encodes the constant region of mu; separate gene segments encode the alternative carboxy termini. It is thought that the two forms of mu are produced by alternative RNA splicing of a single primary transcript. We have used mouse tumor cells that express both membrane (mIgM) and secretable (sIgM) forms. From these cells we have immunoselected more than 50 variants that no longer express the mIgM. Fourteen of these have been extensively characterized with respect to rate, amount, stability, and glycosylation of mum and mus protein and amount and rate of mRNA encoding mum and mus. One variant has suffered a large deletion of part of chromosome 12 and, therefore, synthesizes only the "sterile transcript" that initiates in the J-Cmu intron of the unrearranged homologue. All other variants have patterns on Southern blots that are identical to wildtype. Two variants that have altered proteins have been identified, but each affects both mum and mus. Three variants show no detectable mu protein synthesis and only "sterile" cytoplasmic mu transcripts. However, their rate of transcription in mu is only slightly lower than wildtype. The analysis of the RNA processing and DNA sequence of these variants and selection of new variants with specific phenotypes are currently in progress. We have begun to produce in vitro specific mutations of cloned mu genes. The two membrane-specific gene segments from membrane mu have been fused with the gene segments which encode the extracellular portions of a "reporter protein" (part of a murine major histocompatibility complex class I gene). This construction has been reintroduced into cultured cells to monitor its behavior as a membrane protein. It will be further modified to identify regions of the molecule critical for membrane expression. (CS)