Studies Of Immunoglobulin Gene Rearrangement

在淋巴发育过程中，功能性免疫球蛋白和T细胞受体基因通过一种称为V(D)J重组的过程从基因片段组装而来，这是产生多样化免疫反应所必需的。在这个反应的第一阶段，RAG1/RAG2蛋白复合体在目标位置(RSS)进行特定的双链断裂。重新连接所需的后续步骤使用了许多蛋白质因子，这些蛋白质因子也用于修复X射线损伤。我们最近的工作集中在RAG蛋白上。我们发现，启动重组所需的整个RAG1/2组装与单个识别序列结合，互补序列以裸DNA的形式进入该复合体。这种突触复合体的形成被迫通过这一途径；如果RAG1/2在混合前分别与两个序列结合，它就会被抑制。这一途径有助于确保正确的位点对用于重组。 已知RAG-DNA复合体能够将其识别序列转置为第二个DNA。我们现在已经发现了一种新的“反向转座”，其中非特定的DNA被切割，随后被用来攻击识别序列。尽管非特异性DNA只与RAG1/2弱结合，但正是由于细胞中对识别序列的过度依赖，这种反应偶尔会发生，这为淋巴样肿瘤中存在的染色体易位提供了另一种可能的机制。

During lymphoid development, functional immunoglobulin and T cell receptor genes are assembled from gene segments by a process called V(D)J recombination, which is essential for generating the diversity of the immune response. In the first stage of this reaction, specific double-strand breaks are made at the target sites (RSS) by the RAG1/RAG2 protein complex. The later steps necessary for rejoining employ many protein factors that are also used for repair of X-ray damage. Our recent work has concentrated on the RAG proteins. We show that the whole RAG1/2 assembly necessary to start recombination binds to a single recognition sequence, and the complementary sequence enters this complex as naked DNA. Formation of this synaptic complex is forced to go by this route; it is inhibited if RAG1/2 binds the two sequences separately prior to mixing. This pathway helps to ensure that correct pairs of sites are used for recombination. A RAG-DNA complex is known to be capable of transposing its recognition sequences into a second DNA. We have now found a new kind of ?inverse transposition?, in which non-specific DNA is cleaved and subsequently used to attack a recognition sequence. Although non-specific DNA is bound only weakly by RAG1/2, it is in such excess in cells over the recognition sequences that this reaction may happen occasionally, providing another possible mechanism for chromosomal translocations present in lymphoid tumors.