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疾病，以小头畸形、生长迟缓、严重联合免疫缺陷和淋巴癌高发为特征。NBS患者的细胞表现出染色体不稳定性，对电离辐射过敏，以及辐射后异常的细胞周期调节。我们绘制了。通过微细胞介导的染色体转移进行功能互补分析，在8 q21 -24处检测NBS基因。在NBS细胞系中，只有染色体8 q的一个片段补充了对电离辐射的敏感性。然后，我们在NBS细胞中成功地进行了YAC互补，并将NBS关键区域大幅缩小到800 kb的间隔。最后，我们确定了NBS 1基因，该基因在NBS患者中发生突变。5 bp缺失（657- 661 delACAAA）为创始突变。该基因长50 kb，编码754个氨基酸。与酵母Xrs 2蛋白的N-末端区域的弱同源性被鉴定。睾丸中2.6 kb转录物的表达增强。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.