Casein Kinase II Phosphorylation of Spt6 Enforces Transcriptional Fidelity by Maintaining Spn1-Spt6 Interaction

Spt6 is a histone chaperone that associates with RNA polymerase II and deposits nucleosomes in the wake of transcription. Although Spt6 has an essential function in nucleosome deposition, it is not known whether this function is regulated by post-translational modification. Here, we report that casein kinase II (CKII) phosphorylation of Spt6 directs nucleosome reassembly at the 5' ends of a broad range of genes to prevent aberrant antisense transcription and enforce transcriptional directionality. Mechanistically, we show that interaction of Spt6 with Spn1 – a constitutive binding partner required for chromatin reassembly and full recruitment of Spt6 to genes is positively regulated by CKII phosphorylation of Spt6. Together, our study defines a previously unknown function for CKII phosphorylation in transcription, and further, highlights the importance of post-translational modification as a mechanism to fine-tune the functions of histone chaperones. Overall design: Understanding the role of Spt6 phosphorylation by Casein kinase 2 and the role of such phosphorylation in the regulation of biological functions of Spt6Spt6是一种组蛋白伴侣（histone chaperone），可与RNA聚合酶II（RNA polymerase II）结合，并在转录进程的后方沉积核小体。尽管Spt6在核小体沉积过程中发挥着不可或缺的功能，但其功能是否受翻译后修饰调控仍未明确。本研究发现，酪蛋白激酶II（casein kinase II，CKII）对Spt6的磷酸化修饰，可指导大量基因5'端区域的核小体重组装，从而阻断异常反义转录的发生，并维持转录的方向性。从机制层面来看，本研究证实，Spt6与Spn1——一种参与染色质重组装、并可协助Spt6完整招募至基因位点的组成型结合伴侣——的相互作用，可通过Spt6的CKII磷酸化得到正向调控。综上，本研究阐明了CKII磷酸化在转录过程中一项此前未被发现的功能，并进一步凸显了翻译后修饰作为微调组蛋白伴侣功能的关键机制的重要性。整体实验设计：探究酪蛋白激酶2介导的Spt6磷酸化作用，以及该磷酸化修饰在调控Spt6生物学功能中所发挥的作用。