Zhang Haihua, Freudenreich Catherine H
Department of Biology, Tufts University, Medford, MA 02155, USA.
Mol Cell. 2007 Aug 3;27(3):367-79. doi: 10.1016/j.molcel.2007.06.012.
Common fragile sites are regions of human chromosomes prone to breakage. Fragile site FRA16D spans the WWOX/FOR tumor suppressor gene and has been linked to cancer-causing deletions and translocations. Using a genetic assay in yeast, we found that a short AT-rich region (Flex1) within FRA16D increases chromosome fragility, whereas three other sequences within FRA16D do not. To our knowledge, this is the first identification of a sequence element within a common fragile site that increases chromosome fragility. The fragility of Flex1 was exacerbated by the absence of Rad52 or the presence of hydroxyurea. Flex1 contains a polymorphic AT repeat predicted to form a DNA structure, and two-dimensional gel analysis showed accumulation of stalled replication forks at the Flex1 sequence that was dependent on AT length. Our data suggest that the FRA16D Flex1 sequence causes increased chromosome breakage by forming secondary structures that stall replication fork progression.
常见脆性位点是人类染色体中易于断裂的区域。脆性位点FRA16D跨越WWOX/FOR肿瘤抑制基因，并且与致癌性缺失和易位有关。通过在酵母中进行的基因检测，我们发现FRA16D内的一个富含AT的短区域（Flex1）会增加染色体脆性，而FRA16D内的其他三个序列则不会。据我们所知，这是首次在常见脆性位点内鉴定出增加染色体脆性的序列元件。Rad52缺失或羟基脲的存在会加剧Flex1的脆性。Flex1包含一个预测会形成DNA结构的多态性AT重复序列，二维凝胶分析显示在Flex1序列处停滞的复制叉积累，这取决于AT长度。我们的数据表明，FRA16D Flex1序列通过形成使复制叉前进停滞的二级结构导致染色体断裂增加。
