Department of Microbiology, College of Medicine, National Taiwan University, Taipei, Taiwan.
Nucleic Acids Res. 2010 Jan;38(2):488-98. doi: 10.1093/nar/gkp1008. Epub 2009 Nov 11.
BLM and WRN are members of the RecQ family of DNA helicases, and in humans their loss is associated with syndromes characterized by genome instability and cancer predisposition. As the only RecQ DNA helicase in the yeast Saccharomyces cerevisiae, Sgs1 is known to safeguard genome integrity through its role in DNA recombination. Interestingly, WRN, BLM and Sgs1 are all known to be modified by the small ubiquitin-related modifier (SUMO), although the significance of this posttranslational modification remains elusive. Here, we demonstrate that Sgs1 is specifically sumoylated under the stress of DNA double strand breaks. The major SUMO attachment site in Sgs1 is lysine 621, which lies between the Top3 binding domain and the DNA helicase domain. Surprisingly, sumoylation of K621 was found to be uniquely required for Sgs1's role in telomere-telomere recombination. In contrast, sumoylation was dispensable for Sgs1's roles in DNA damage tolerance, supppression of direct repeat and rDNA recombination, and promotion of top3Delta slow growth. Our results demonstrate that although modification by SUMO is a conserved feature of RecQ family DNA helicases, the major sites of modification are located on different domains of the protein in different organisms. We suggest that sumoylation of different domains of RecQ DNA helicases from different organisms contributes to conserved roles in regulating telomeric recombination.
BLM 和 WRN 是 RecQ 家族 DNA 解旋酶的成员，在人类中，它们的缺失与基因组不稳定和癌症易感性相关的综合征有关。作为酵母酿酒酵母中唯一的 RecQ DNA 解旋酶，Sgs1 已知通过其在 DNA 重组中的作用来保护基因组完整性。有趣的是，WRN、BLM 和 Sgs1 都已知被小泛素相关修饰物（SUMO）修饰，尽管这种翻译后修饰的意义仍然难以捉摸。在这里，我们证明 Sgs1 在 DNA 双链断裂的应激下被特异性 SUMO 化。Sgs1 中的主要 SUMO 附着位点是赖氨酸 621，它位于 Top3 结合域和 DNA 解旋酶域之间。令人惊讶的是，发现 K621 的 SUMO 化对于 Sgs1 在端粒-端粒重组中的作用是唯一必需的。相比之下，SUMO 化对于 Sgs1 在 DNA 损伤容忍、直接重复和 rDNA 重组的抑制以及 top3Delta 生长缓慢的促进作用是可有可无的。我们的结果表明，尽管 SUMO 的修饰是 RecQ 家族 DNA 解旋酶的保守特征，但修饰的主要位点位于不同生物体中蛋白质的不同结构域上。我们建议，来自不同生物体的 RecQ DNA 解旋酶的不同结构域的 SUMO 化有助于调节端粒重组的保守作用。
