Köhler G, Potash M J, Lehrach H, Shulman M J
EMBO J. 1982;1(5):555-63. doi: 10.1002/j.1460-2075.1982.tb01208.x.
Eight mutant hybridoma lines are described, which synthesize short immunoglobulin mu chains. Four internal deletions were mapped by Southern blot analysis. They are shown to remove DNA from either part or all of the first, and first and second, constant mu exons. The sizes of the deletions range between 0.6 and 5 kb, leaving an equal or unequal number of splice signals. Shorter mu RNA of one size was found irrespective of whether an exon was completely or only partially deleted. These results preclude exclusive 3' (constant region) to 5' (variable region) directional splicing of the mu RNA. No important signals seem to reside in the deleted DNA stretches affecting the transcription or the correct RNA splicing of the remaining exons. The internal mu protein deletions revealed unusual covalent light chain attachment demonstrating functional homology between the first (normally used) and fourth mu constant domain. The other mu protein deletions (10, 11, and 12 kd) involved neither gross DNA nor RNA lesions and are considered to be due to premature chain termination. Since secretion is found in most of the mutant IgM-producing lines, no single one of the four mu constant domains (including the C-terminal one which contains the so-called secretory piece) is necessary for secretion.
本文描述了八个可合成短免疫球蛋白μ链的突变杂交瘤细胞系。通过Southern印迹分析对四个内部缺失进行了定位。结果表明，这些缺失会从第一个恒定μ外显子的部分或全部，以及第一个和第二个恒定μ外显子中去除DNA。缺失的大小在0.6至5 kb之间，留下数量相等或不等的剪接信号。无论外显子是完全缺失还是仅部分缺失，都发现了一种大小的较短μRNA。这些结果排除了μRNA从3'（恒定区）到5'（可变区）的单向剪接。在缺失的DNA片段中似乎没有重要信号影响剩余外显子的转录或正确的RNA剪接。内部μ蛋白缺失显示出异常的共价轻链连接，表明第一个（通常使用的）和第四个μ恒定结构域之间存在功能同源性。其他μ蛋白缺失（10、11和12 kd）既不涉及大片段DNA也不涉及RNA损伤，被认为是由于链的提前终止。由于在大多数产生突变IgM的细胞系中都发现了分泌现象，因此四个μ恒定结构域中的任何一个（包括含有所谓分泌片段的C末端结构域）都不是分泌所必需的。
