Spt6 association with RNAPII directs mRNA turnover during transcription. Spt6 association with RNAPII directs mRNA turnover during transcription

Spt6 is an essential histone chaperone that mediates nucleosome reassembly during gene transcription. Spt6 interacts with elongating RNA polymerase II (RNAPII) via a tandem Src2 homology (tSH2) domain, but it is not known whether this particular interaction is required for the nucleosome reassembly activity of Spt6. Here, we show that Spt6 recruitment to genes and its nucleosome reassembly functions are largely independent of association with RNAPII. Instead, the Spt6-RNAPII association is required for post-transcriptional mRNA turnover. Mechanistically, association of Spt6 with RNAPII couples the Ccr4-Not complex to the transcribed regions of genes, which we show regulates the timely deadenylation and degradation of a broad range of mRNAs including those required for cell cycle progression. Thus, our findings reveal an unexpected control mechanism for mRNA turnover facilitated by a histone chaperone during transcription. Overall design: RNA-seq (3 replicates) and ATAC-seq (3 replicates), along with other biochemical assays, were performed on WT vs tSH2 mutants of Spt6 to understanding the role of Spt6 in regulation of mRNA stability in yeast.

Spt6是一种必需的组蛋白伴侣（histone chaperone），可在基因转录过程中介导核小体重组装。Spt6通过串联Src2同源结构域（tandem Src2 homology domain, tSH2）与延伸中的RNA聚合酶II（RNA polymerase II, RNAPII）发生相互作用，但目前尚不明确这一特定相互作用是否为Spt6的核小体重组装活性所必需。本研究表明，Spt6在基因位点的招募及其核小体重组装功能，在很大程度上不依赖于与RNAPII的结合。与之相反，Spt6与RNAPII的结合是转录后mRNA周转过程所必需的。从机制层面而言，Spt6与RNAPII的结合可将Ccr4-Not复合物（Ccr4-Not complex）招募至基因的转录区域，本研究证实该过程可调控包括细胞周期进程相关基因在内的广泛mRNA的及时脱腺苷化与降解。因此，本研究揭示了一种由组蛋白伴侣在转录过程中介导的、此前未被发现的mRNA周转调控机制。总体实验设计：本研究对酵母Spt6的野生型（wild type, WT）与tSH2结构域突变体开展了3次生物学重复的RNA测序（RNA-seq）、转座酶可及性测序（ATAC-seq）及其他生化实验，以解析Spt6在酵母mRNA稳定性调控中的作用。