The Shmunis School of Biomedicine & Cancer Research, Tel Aviv University, Israel.
PLoS Genet. 2021 Feb 18;17(2):e1009391. doi: 10.1371/journal.pgen.1009391. eCollection 2021 Feb.
During DNA replication newly synthesized histones are incorporated into the chromatin of the replicating sister chromatids. In the yeast Saccharomyces cerevisiae new histone H3 molecules are acetylated at lysine 56. This modification is carefully regulated during the cell cycle, and any disruption of this process is a source of genomic instability. Here we show that the protein kinase Dun1 is necessary in order to maintain viability in the absence of the histone deacetylases Hst3 and Hst4, which remove the acetyl moiety from histone H3. This lethality is not due to the well-characterized role of Dun1 in upregulating dNTPs, but rather because Dun1 is needed in order to counteract the checkpoint kinase Rad53 (human CHK2) that represses the activity of late firing origins. Deletion of CTF18, encoding the large subunit of an alternative RFC-like complex (RLC), but not of components of the Elg1 or Rad24 RLCs, is enough to overcome the dependency of cells with hyper-acetylated histones on Dun1. We show that the detrimental function of Ctf18 depends on its interaction with the leading strand polymerase, Polε. Our results thus show that the main problem of cells with hyper-acetylated histones is the regulation of their temporal and replication programs, and uncover novel functions for the Dun1 protein kinase and the Ctf18 clamp loader.
在 DNA 复制过程中，新合成的组蛋白被掺入到复制姐妹染色单体的染色质中。在酵母酿酒酵母中，新的组蛋白 H3 分子在赖氨酸 56 处乙酰化。这种修饰在细胞周期中受到严格调控，任何对这个过程的干扰都是基因组不稳定的来源。在这里，我们表明，蛋白激酶 Dun1 对于在没有组蛋白去乙酰化酶 Hst3 和 Hst4 的情况下维持生存能力是必要的，Hst3 和 Hst4 从组蛋白 H3 上除去乙酰基。这种致死性不是由于 Dun1 在上调 dNTPs 方面的作用，而是因为 Dun1 是为了抵消检查点激酶 Rad53（人 CHK2）的需要，Rad53 抑制晚期启动原点的活性。删除编码替代 RFC 样复合物（RLC）的大亚基的 CTF18，但不删除 Elg1 或 Rad24 RLC 的成分，足以克服对 Dun1 具有超乙酰化组蛋白的细胞的依赖性。我们表明，Ctf18 的有害功能取决于它与前导链聚合酶 Polε 的相互作用。因此，我们的结果表明，具有超乙酰化组蛋白的细胞的主要问题是它们的时间和复制程序的调节，并揭示了 Dun1 蛋白激酶和 Ctf18 夹加载器的新功能。
