Complementation assisted positional cloning of the gene for AT variant.

奈梅金综合征是一种常染色体隐性遗传病，以小头畸形、生长迟缓、严重的联合免疫缺陷和淋巴癌的高发病率为特征。NBS患者的细胞在照射后表现出染色体不稳定、对电离辐射敏感和细胞周期调节异常。我们绘制了地图。利用微细胞介导的染色体转移功能互补分析8q21-24的NBS基因。在NBS细胞系中，只有染色体8q的一段片段补充了对电离辐射的敏感性。然后，我们成功地在NBS细胞中进行了YAC互补，并将NBS关键区域大幅缩小到800kb的区间。最后，我们鉴定了在NBS患者中发生突变的NBS1基因。缺失5个碱基的657-661delACAAA为方正突变。该基因全长50kb，编码754个氨基酸的蛋白质。N-末端与酵母Xrs2蛋白有弱同源性。2.6kb转录本在睾丸中的表达增强。这些结果表明NBSM基因可能参与减数分裂重组。

Nijmegen syndrome is an autosomal recessive disorder characterized by microcephaly, growth retardation, severe combined immunodeficiency, and a high incidence of lymphoid cancers. Cells from NBS patients display chromosome instability, hypersensitivity to ionizing radiation, and an abnormal cell cycle regulation after irradiation. We mapped the. NBS gene at 8q21-24 by functional complementation assays using microcell-mediated chromosome transfer. Only a fragment of chromosome 8q complemented the sensitivity to ionizing radiation in NBS cell lines. We then succeeded in YAC complementation in the NBS cell, and substantially narrowed the NBS critical region to an 800 kb interval. Finally, we identified the NBS1 gene, which is mutated in NBS patients. The 5-bp-deletion, 657-661delACAAA, was found to be founder mutation. The gene is 50 kb long and encodes a protein of 754 amino acids. A weak homology in the N-terminal region was identified with the yeast Xrs2 proteins. Expression of the 2.6 kb transcripts is enhanced in the testis. These results suggested that the NBSM gene might be involved in meiotic recombination.