Laboratory of Genome Regeneration, Institute for Quantitative Biosciences (IQB), Bunkyo-ku, Japan.
Institute of Molecular and Cellular Biosciences, The University of Tokyo, Bunkyo-ku, Japan.
PLoS Genet. 2019 Apr 18;15(4):e1008103. doi: 10.1371/journal.pgen.1008103. eCollection 2019 Apr.
The ribosomal RNA genes (rDNA) comprise a highly repetitive gene cluster. The copy number of genes at this locus can readily change and is therefore one of the most unstable regions of the genome. DNA damage in rDNA occurs after binding of the replication fork blocking protein Fob1 in S phase, which triggers unequal sister chromatid recombination. However, the precise mechanisms by which such DNA double-strand breaks (DSBs) are repaired is not well understood. Here, we demonstrate that the conserved protein kinase Tel1 maintains rDNA stability after replication fork arrest. We show that rDNA associates with nuclear pores, which is dependent on DNA damage checkpoint kinases Mec1/Tel1 and replisome component Tof1. These findings suggest that rDNA-nuclear pore association is due to a replication fork block and subsequent DSB. Indeed, quantitative microscopy revealed that rDNA is relocated to the nuclear periphery upon induction of a DSB. Finally, rDNA stability was reduced in strains where this association with the nuclear envelope was prevented, which suggests its importance for avoiding improper recombination repair that could induce repeat instability.
核糖体 RNA 基因（rDNA）包含一个高度重复的基因簇。该基因座的基因拷贝数很容易发生变化，因此是基因组中最不稳定的区域之一。在 S 期，复制叉阻断蛋白 Fob1 结合后，rDNA 中会发生 DNA 损伤，从而引发不等姐妹染色单体重组。然而，对于这种 DNA 双链断裂（DSB）的修复机制，我们还不是很了解。在这里，我们证明了保守的蛋白激酶 Tel1 在复制叉停滞后维持 rDNA 的稳定性。我们表明 rDNA 与核孔相关，这依赖于 DNA 损伤检查点激酶 Mec1/Tel1 和复制体成分 Tof1。这些发现表明，rDNA-核孔的关联是由于复制叉受阻和随后的 DSB。事实上，定量显微镜显示，在诱导 DSB 后，rDNA 被重新定位到核周。最后，在阻止与核膜这种关联的菌株中，rDNA 的稳定性降低，这表明这种关联对于避免可能导致重复不稳定的不当重组修复非常重要。
