Shulman M J, Pennell N, Collins C, Hozumi N
Proc Natl Acad Sci U S A. 1986 Oct;83(20):7678-82. doi: 10.1073/pnas.83.20.7678.
We have isolated and analyzed the DNA encoding the mu heavy chain constant region of a mutant IgM that is defective in initiating complement-dependent cytolysis. By assaying the expression of mu-chain genes that were constructed in vitro from mutant and wild-type gene segments, we have mapped the mutation into a 555-base-pair segment that spans part of the third and fourth constant region domains. In this segment there is one nucleotide change, such that the mutant mu-chain gene encodes asparagine rather than the normal serine at amino acid position 406 in the third constant domain. We have used site-directed mutagenesis to introduce a comparable mutation into the normal mu-chain gene and confirmed that this substitution causes the production of IgM with the original mutant phenotype. Evidence is also provided that the serine-406----asparagine substitution might cause the mutant mu chain to be abnormally glycosylated.
我们已经分离并分析了编码一种突变型IgM的μ重链恒定区的DNA，该突变型IgM在启动补体依赖性细胞溶解方面存在缺陷。通过检测由突变型和野生型基因片段体外构建的μ链基因的表达，我们已将该突变定位到一个555个碱基对的片段中，该片段跨越第三和第四恒定区结构域的一部分。在这个片段中有一个核苷酸变化，使得突变型μ链基因在第三恒定结构域的氨基酸位置406处编码天冬酰胺而非正常的丝氨酸。我们利用定点诱变技术在正常μ链基因中引入了一个类似的突变，并证实这种取代导致产生具有原始突变表型的IgM。同时也提供了证据表明丝氨酸406突变为天冬酰胺可能导致突变型μ链异常糖基化。
