Meetei Amom Ruhikanta, Sechi Salvatore, Wallisch Michael, Yang Dafeng, Young Mary K, Joenje Hans, Hoatlin Maureen E, Wang Weidong
Laboratory of Genetics. Mass Spectrometry Unit, National Institute on Aging/NIH, TRIAD Center Room 3000, 333 Cassell Drive, Baltimore, MD 21224, USA.
Mol Cell Biol. 2003 May;23(10):3417-26. doi: 10.1128/MCB.23.10.3417-3426.2003.
Bloom syndrome (BS) is a genetic disorder associated with dwarfism, immunodeficiency, reduced fertility, and an elevated risk of cancer. To investigate the mechanism of this disease, we isolated from human HeLa extracts three complexes containing the helicase defective in BS, BLM. Interestingly, one of the complexes, termed BRAFT, also contains five of the Fanconi anemia (FA) complementation group proteins (FA proteins). FA resembles BS in genomic instability and cancer predisposition, but most of its gene products have no known biochemical activity, and the molecular pathogenesis of the disease is poorly understood. BRAFT displays a DNA-unwinding activity, which requires the presence of BLM because complexes isolated from BLM-deficient cells lack such an activity. The complex also contains topoisomerase IIIalpha and replication protein A, proteins that are known to interact with BLM and could facilitate unwinding of DNA. We show that BLM complexes isolated from an FA cell line have a lower molecular mass. Our study provides the first biochemical characterization of a multiprotein FA complex and suggests a connection between the BLM and FA pathways of genomic maintenance. The findings that FA proteins are part of a DNA-unwinding complex imply that FA proteins may participate in DNA repair.
布卢姆综合征（BS）是一种与侏儒症、免疫缺陷、生育力下降和癌症风险升高相关的遗传性疾病。为了研究这种疾病的发病机制，我们从人HeLa细胞提取物中分离出三种含有布卢姆综合征中解旋酶缺陷蛋白BLM的复合物。有趣的是，其中一种复合物称为BRAFT，还包含五种范可尼贫血（FA）互补组蛋白（FA蛋白）。FA在基因组不稳定性和癌症易感性方面与BS相似，但其大多数基因产物没有已知的生化活性，该疾病的分子发病机制也知之甚少。BRAFT具有DNA解旋活性，这需要BLM的存在，因为从BLM缺陷细胞中分离出的复合物缺乏这种活性。该复合物还包含拓扑异构酶IIIα和复制蛋白A，已知这些蛋白可与BLM相互作用并促进DNA解旋。我们发现从FA细胞系中分离出的BLM复合物分子量较低。我们的研究首次对一种多蛋白FA复合物进行了生化表征，并表明BLM和FA基因组维持途径之间存在联系。FA蛋白是DNA解旋复合物一部分的发现意味着FA蛋白可能参与DNA修复。
