Department of Biochemistry and Molecular Biology, Louisiana State University Health Sciences Center, Shreveport, LA 71130, United States.
Department of Biochemistry and Molecular Biology, Louisiana State University Health Sciences Center, Shreveport, LA 71130, United States.
Gene. 2024 Aug 5;918:148473. doi: 10.1016/j.gene.2024.148473. Epub 2024 Apr 13.
How gene activation works in heterochromatin, and how the mechanism might differ from the one used in euchromatin, has been largely unexplored. Previous work has shown that in SIR-regulated heterochromatin of Saccharomyces cerevisiae, gene activation occurs in the absence of covalent histone modifications and other alterations of chromatin commonly associated with transcription.Here we demonstrate that such activation occurs in a substantial fraction of cells, consistent with frequent transcriptional bursting, and this raises the possibility that an alternative activation pathway might be used. We address one such possibility, Pol II CTD phosphorylation, and explore this idea using a natural telomere-linked gene, YFR057w, as a model. Unlike covalent histone modifications, we find that Ser2, Ser5 and Ser7 CTD phosphorylated Pol II is prevalent at the drug-induced heterochromatic gene. Particularly enriched relative to the euchromatic state is Ser2 phosphorylation. Consistent with a functional role for Ser2P, YFR057w is negligibly activated in cells deficient in the Ser2 CTD kinases Ctk1 and Bur1 even though the gene is strongly stimulated when it is placed in a euchromatic context. Collectively, our results are consistent with a critical role for Ser2 CTD phosphorylation in driving Pol II recruitment and transcription of a natural heterochromatic gene - an activity that may supplant the need for histone epigenetic modifications.
基因激活在异染色质中是如何工作的，以及其机制与常染色质中的机制有何不同，在很大程度上还没有得到探索。以前的工作表明，在酿酒酵母的 SIR 调控的异染色质中，基因激活发生在没有组蛋白共价修饰和其他通常与转录相关的染色质改变的情况下。在这里，我们证明这种激活发生在相当一部分细胞中，与频繁的转录爆发一致，这就提出了可能使用替代激活途径的可能性。我们研究了一种这样的可能性，即 Pol II CTD 磷酸化，并使用一个自然的端粒连接基因 YFR057w 作为模型来探索这个想法。与组蛋白共价修饰不同，我们发现 Ser2、Ser5 和 Ser7 CTD 磷酸化的 Pol II 在药物诱导的异染色质基因中普遍存在。与常染色质状态相比，Ser2 磷酸化特别丰富。与 Ser2P 的功能作用一致，即使将该基因置于常染色质环境中，在缺乏 Ser2 CTD 激酶 Ctk1 和 Bur1 的细胞中，YFR057w 的基因几乎没有被激活，尽管该基因受到强烈的刺激。总的来说，我们的结果与 Ser2 CTD 磷酸化在驱动 Pol II 募集和天然异染色质基因转录中的关键作用一致——这种活性可能取代了组蛋白表观遗传修饰的需求。
