m6A reader Pho92 is recruited co-transcriptionally and couples translation efficacy to mRNA decay to promote meiotic fitness in yeast [iCLIP_miCLIP-seq]

During meiosis, in Saccharomyces cerevisiae, N6-methyladenosine (m6A) modified transcripts are induced, of which the function is unknown. Here, we uncover the role of the m6A reader Pho92. Cross-linking immunoprecipitation (CLIP) revealed that Pho92 associates with meiotic mRNAs in both m6A dependent and independent manner. Incidentally, Pho92 resides in the nucleus during early meiosis and associates with nascent RNAs, which is mediated through its interaction with Paf1C. Transcripts bound by Pho92 show elevated translational efficiency while cells lacking Pho92 display a small, but notable, increase in mRNA levels but not in protein levels, suggesting role of Pho92 in translation and decay. We show that Pho92 associates with ribosomes where it promotes the decay of m6A modified transcripts, contingent on active translation and the CCR4-NOT complex. We propose that m6A reader Pho92 is loaded co-transcriptionally to promote translation and subsequent decay fate of m6A modified transcripts, which ensures gamete fitness.在减数分裂过程中，酿酒酵母（Saccharomyces cerevisiae）内会诱导产生N6-甲基腺苷（N6-methyladenosine，m6A）修饰的转录本，但其功能至今尚未明确。本研究揭示了m6A识别蛋白（m6A reader）Pho92的生物学作用。交联免疫沉淀（Cross-linking immunoprecipitation，CLIP）实验结果显示，Pho92可通过m6A依赖与非依赖两种方式与减数分裂相关mRNA相结合。值得注意的是，Pho92在减数分裂早期定位于细胞核，并可与新生RNA结合，这一过程由其与PAF1复合物（Paf1C）的相互作用所介导。被Pho92结合的转录本表现出翻译效率升高；而缺失Pho92的细胞则出现mRNA水平小幅但显著的上升，但蛋白水平并无变化，这提示Pho92在翻译调控及mRNA降解过程中发挥功能。本研究证实，Pho92可与核糖体结合，进而促进m6A修饰转录本的降解，这一过程依赖于活跃的翻译进程及CCR4-NOT复合物（CCR4-NOT complex）。我们提出，m6A识别蛋白Pho92可共转录加载，以促进m6A修饰转录本的翻译及后续降解命运，从而保障配子的适合度。