Institute of Biochemical Sciences, National Taiwan University, No. 1, Section 4, Roosevelt Road, Taipei, 10617, Taiwan.
Nucleic Acids Res. 2012 Aug;40(14):6558-69. doi: 10.1093/nar/gks305. Epub 2012 Apr 9.
Homologous recombination (HR) represents a major error-free pathway to eliminate pre-carcinogenic chromosomal lesions. The DNA strand invasion reaction in HR is mediated by a helical filament of the Rad51 recombinase assembled on single-stranded DNA that is derived from the nucleolytic processing of the primary lesion. Recent studies have found that the human and mouse Swi5 and Sfr1 proteins form a complex that influences Rad51-mediated HR in cells. Here, we provide biophysical evidence that the mouse Swi5-Sfr1 complex has a 1:1 stoichiometry. Importantly, the Swi5-Sfr1 complex, but neither Swi5 nor Sfr1 alone, physically interacts with Rad51 and stimulates Rad51-mediated homologous DNA pairing. This stimulatory effect stems from the stabilization of the Rad51-ssDNA presynaptic filament. Moreover, we provide evidence that the RSfp (rodent Sfr1 proline rich) motif in Sfr1 serves as a negative regulatory element. These results thus reveal an evolutionarily conserved function in the Swi5-Sfr1 complex and furnish valuable information as to the regulatory role of the RSfp motif that is specific to the mammalian Sfr1 orthologs.
同源重组 (HR) 代表了一种主要的无错误途径，可以消除致癌前的染色体损伤。HR 中的 DNA 链入侵反应是由 Rad51 重组酶在单链 DNA 上组装的螺旋丝介导的，该单链 DNA 来自初级损伤的核酸内切加工。最近的研究发现，人和鼠的 Swi5 和 Sfr1 蛋白形成一个复合物，影响细胞中 Rad51 介导的 HR。在这里，我们提供了生物物理证据，证明小鼠 Swi5-Sfr1 复合物具有 1:1 的化学计量比。重要的是，Swi5-Sfr1 复合物，但不是 Swi5 或 Sfr1 单独，与 Rad51 物理相互作用并刺激 Rad51 介导的同源 DNA 配对。这种刺激作用源于 Rad51-ssDNA 前突触丝的稳定。此外，我们提供的证据表明，Sfr1 中的 RSfp（啮齿动物 Sfr1 脯氨酸丰富）基序作为一个负调节元件。这些结果因此揭示了 Swi5-Sfr1 复合物中保守的功能，并为哺乳动物 Sfr1 同源物特有的 RSfp 基序的调节作用提供了有价值的信息。
