Complementation assisted positional cloning of the gene for AT variant.

奈梅亨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样癌的高发为特征。NBS患者的细胞表现出染色体不稳定，对电离辐射过敏，辐照后细胞周期调节异常。我们映射了。利用微细胞介导的染色体转移对NBS基因8q21-24进行功能性互补检测。在NBS细胞系中，只有一个8q染色体片段与电离辐射敏感性互补。然后，我们成功地在NBS细胞中实现了YAC互补，并将NBS关键区域大大缩小到800kb的间隔。最后，我们确定了在NBS患者中发生突变的NBS1基因。5 bp缺失657-661delACAAA为始创突变。该基因长50 kb，编码一种含有754个氨基酸的蛋白质。在n端与酵母Xrs2蛋白有弱同源性。2.6 kb转录本的表达在睾丸中增强。这些结果提示NBSM基因可能参与了减数分裂重组。

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.