Cell division is thought to be initiated by cyclin-dependent kinases (Cdks) inactivating key transcriptional inhibitors. In budding yeast, the G₁ cyclin Cln3-Cdk1 complex is thought to directly phosphorylate the Whi5 protein, thereby releasing the transcription factor SBF and committing cells to division. We report that Whi5 is a poor substrate of Cln3-Cdk1, which instead phosphorylates the RNA polymerase II subunit Rpb1’s C-terminal domain on S₅ of its heptapeptide repeats. Cln3-Cdk1 binds SBF-regulated promoters and Cln3’s function can be performed by the canonical S₅ kinase Ccl1-Kin28 when synthetically recruited to SBF. Thus, we propose that Cln3-Cdk1 triggers cell division by phosphorylating Rpb1 at SBF-regulated promoters to promote transcription. Our findings blur the distinction between cell cycle and transcriptional Cdks to highlight the ancient relationship between these two processes.

中文翻译：

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G1 细胞周期蛋白-Cdk 通过 RNA 聚合酶 II 的局部磷酸化促进细胞周期进入


细胞分裂被认为是由细胞周期蛋白依赖性激酶 (Cdks) 失活关键转录抑制剂启动的。在芽殖酵母中，G ₁细胞周期蛋白 Cln3-Cdk1 复合物被认为可以直接磷酸化 Whi5 蛋白，从而释放转录因子 SBF 并使细胞分裂。我们报告说，Whi5 是 Cln3-Cdk1 的不良底物，它会磷酸化 RNA 聚合酶 II 亚基 Rpb1 七肽重复序列 S ₅上的 C 端结构域。 Cln3-Cdk1 结合 SBF 调节的启动子，当合成招募至 SBF 时，Cln3 的功能可由经典 S ₅激酶 Ccl1-Kin28 来执行。因此，我们提出 Cln3-Cdk1 通过在 SBF 调节的启动子处磷酸化 Rpb1 来触发细胞分裂，从而促进转录。我们的研究结果模糊了细胞周期和转录 Cdks 之间的区别，以强调这两个过程之间的古老关系。