Burton Peter, McBride David J, Wilkes Jonathan M, Barry J David, McCulloch Richard
The Wellcome Centre for Molecular Parasitology, University of Glasgow, Glasgow Biomedical Research Centre, Glasgow, Scotland, UK.
Eukaryot Cell. 2007 Oct;6(10):1773-81. doi: 10.1128/EC.00212-07. Epub 2007 Aug 10.
DNA double-strand breaks (DSBs) are repaired primarily by two distinct pathways: homologous recombination and nonhomologous end joining (NHEJ). NHEJ has been found in all eukaryotes examined to date and has been described recently for some bacterial species, illustrating its ancestry. Trypanosoma brucei is a divergent eukaryotic protist that evades host immunity by antigenic variation, a process in which homologous recombination plays a crucial function. While homologous recombination has been examined in some detail in T. brucei, little work has been done to examine what other DSB repair pathways the parasite utilizes. Here we show that T. brucei cell extracts support the end joining of linear DNA molecules. These reactions are independent of the Ku heterodimer, indicating that they are distinct from NHEJ, and are guided by sequence microhomology. We also demonstrate bioinformatically that T. brucei, in common with other kinetoplastids, does not encode recognizable homologues of DNA ligase IV or XRCC4, suggesting that NHEJ is either absent or mechanistically diverged in these pathogens.
DNA双链断裂（DSBs）主要通过两种不同的途径进行修复：同源重组和非同源末端连接（NHEJ）。到目前为止，在所有已检测的真核生物中都发现了NHEJ，并且最近在一些细菌物种中也有相关描述，这说明了它的起源。布氏锥虫是一种不同寻常的真核原生生物，它通过抗原变异来逃避宿主免疫，在这个过程中同源重组发挥着关键作用。虽然已经对布氏锥虫中的同源重组进行了一些详细研究，但对于该寄生虫利用的其他DSB修复途径的研究却很少。在这里，我们表明布氏锥虫细胞提取物支持线性DNA分子的末端连接。这些反应不依赖于Ku异源二聚体，表明它们与NHEJ不同，并且由序列微同源性引导。我们还通过生物信息学证明，与其他动基体目生物一样，布氏锥虫不编码可识别的DNA连接酶IV或XRCC4同源物，这表明在这些病原体中要么不存在NHEJ，要么其机制有所不同。
