Han J O, Erskine L A, Purugganan M M, Stamato T D, Roth D B
The Department of Microbiology and Immunology, Baylor College of Medicine and The Howard Hughes Medical Institute, Baylor College of Medicine, Houston, TX 77030, USA.
Nucleic Acids Res. 1998 Aug 15;26(16):3769-75. doi: 10.1093/nar/26.16.3769.
V(D)J recombination assembles immunoglobulin (Ig) and T cell receptor (TCR) gene segments during lymphocyte development. Recombination is initiated by the RAG-1 and RAG-2 proteins, which introduce double-stranded DNA breaks (DSB) adjacent to the Ig and TCR gene segments. The broken ends are joined by the DSB repair machinery, which includes the XRCC4 protein. While XRCC4 is essential for both DSB repair and V(D)J recombination, the functions of this protein remain enigmatic. Because the rare V(D)J recombination products isolated from XRCC4-deficient cells generally show evidence of excessive nucleotide loss, it was hypothesized that XRCC4 may function to protect broken DNA ends. Here we report the first examination of V(D)J recombination intermediates in XRCC4-deficient cells. We found that both types of intermediates, signal ends and coding ends, are abundant in the absence of XRCC4. Furthermore, the signal ends are full length. We also showed that alternative V(D)J recombination products, hybrid joints, form with normal efficiency and without excessive deletion in XRCC4-deficient cells. These data indicate that impaired formation of V(D)J recombination products in XRCC4-deficient cells does not result from excessive degradation of recombination intermediates. Potential roles of XRCC4 in the joining reaction are discussed.
V(D)J重排过程在淋巴细胞发育期间组装免疫球蛋白（Ig）和T细胞受体（TCR）基因片段。重排由RAG-1和RAG-2蛋白启动，它们在Ig和TCR基因片段附近引入双链DNA断裂（DSB）。断裂末端由包括XRCC4蛋白在内的DSB修复机制连接起来。虽然XRCC4对DSB修复和V(D)J重排都至关重要，但该蛋白的功能仍然成谜。由于从XRCC4缺陷细胞中分离出的罕见V(D)J重排产物通常显示出过度核苷酸缺失的证据，因此推测XRCC4可能起到保护断裂DNA末端的作用。在此我们报告了对XRCC4缺陷细胞中V(D)J重排中间体的首次检测。我们发现，在缺乏XRCC4的情况下，两种类型的中间体，即信号末端和编码末端，都大量存在。此外，信号末端是全长的。我们还表明，在XRCC4缺陷细胞中，替代性V(D)J重排产物，即杂交接头，以正常效率形成且没有过度缺失。这些数据表明，XRCC4缺陷细胞中V(D)J重排产物形成受损并非源于重排中间体的过度降解。我们讨论了XRCC4在连接反应中的潜在作用。
