Peters A, Storb U
Department of Biochemistry and Molecular Biology, University of Chicago, Illinois 60637, USA.
Immunity. 1996 Jan;4(1):57-65. doi: 10.1016/s1074-7613(00)80298-8.
To identify DNA sequences that target the somatic hypermutation process, the immunoglobulin gene promoter located upstream of the variable (V) region was duplicated upstream of the constant (C) region of a kappa transgene. Normally, kappa genes are somatically mutated only in the VJ region, but not in the C region. In B cell hybridomas from mice with this kappa transgene (P5'C), both the VJ region and the C region, but not the region between them, were mutated at similar frequencies, suggesting that the mutation mechanism is related to transcription. The downstream promoter was not occluded by transcripts from the upstream promoter. In fact, the levels of transcripts originating from the two promoters were similar, supporting a mutation model based on initiation of transcripts. Several "hot-spots" of somatic mutation were noted, further demonstrating that this transgene has the hallmarks of somatic mutation of endogenous immunoglobulin genes. A model linking somatic mutation to transcription-coupled DNA repair is proposed.
为了鉴定靶向体细胞超突变过程的DNA序列，将位于可变（V）区上游的免疫球蛋白基因启动子复制到κ转基因恒定（C）区的上游。正常情况下，κ基因仅在VJ区发生体细胞突变，而不在C区发生突变。在携带这种κ转基因（P5'C）的小鼠的B细胞杂交瘤中，VJ区和C区均发生了突变，且突变频率相似，但它们之间的区域未发生突变，这表明突变机制与转录有关。下游启动子未被上游启动子的转录本所阻断。事实上，来自两个启动子的转录本水平相似，这支持了基于转录起始的突变模型。观察到了几个体细胞突变的“热点”，进一步证明该转基因具有内源性免疫球蛋白基因体细胞突变的特征。本文提出了一个将体细胞突变与转录偶联DNA修复联系起来的模型。
