BACKGROUND The transition from mitotic cell division to meiotic development in S. cerevisiae requires induction of a transient transcription program that is initiated by Ime1-dependent destruction of the repressor Ume6. Although IME1 mRNA is observed in vegetative cultures, Ime1 protein is not suggesting the presence of a regulatory system restricting translation to meiotic cells. RESULTS This study demonstrates that IME1 mRNA translation requires Rpl22A and Rpl22B, eukaryotic-specific ribosomal protein paralogs of the 60S large subunit. In the absence of Rpl22 function, IME1 mRNA synthesis is normal in cultures induced to enter meiosis. However, Ime1 protein production is reduced and the Ume6 repressor is not destroyed in rpl22 mutant cells preventing early meiotic gene induction resulting in a pre-meiosis I arrest. This role for Rpl22 is not a general consequence of mutating non-essential large ribosomal proteins as strains lacking Rpl29 or Rpl39 execute meiosis with nearly wild-type efficiencies. Several results indicate that Rpl22 functions by enhancing IME1 mRNA translation. First, the Ime1 protein synthesized in rpl22 mutant cells demonstrates the same turnover rate as in wild-type cultures. In addition, IME1 transcript is found in polysome fractions isolated from rpl22 mutant cells indicating that mRNA nuclear export and ribosome association occurs. Finally, deleting the unusually long 5'UTR restores Ime1 levels and early meiotic gene transcription in rpl22 mutants suggesting that Rpl22 enhances translation through this element. Polysome profiles revealed that under conditions of high translational output, Rpl22 maintains high free 60S subunit levels thus preventing halfmer formation, a translation species indicative of mRNAs bound by an unpaired 40S subunit. In addition to meiosis, Rpl22 is also required for invasive and pseudohyphal growth. CONCLUSIONS These findings indicate that Rpl22A and Rpl22B are required to selectively translate IME1 mRNA that is required for meiotic induction and subsequent gametogenesis. In addition, our results imply a more general role for Rpl22 in cell fate switches responding to environmental nitrogen signals.

中文翻译：

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Rpl22是酿酒酵母中IME1 mRNA翻译和减数分裂诱导所必需的。

背景技术酿酒酵母中从有丝分裂细胞分裂到减数分裂发育的转变需要诱导瞬时转录程序，该程序由阻遏物Ume6的Ime1依赖性破坏引发。尽管在营养培养物中观察到IME1 mRNA，但Ime1蛋白并未提示存在限制翻译为减数分裂细胞的调节系统。结果这项研究表明IME1 mRNA翻译需要Rpl22A和Rpl22B，这是60S大亚基的真核生物特异性核糖体蛋白旁系同源物。在没有Rpl22功能的情况下，IME1 mRNA合成在诱导进入减数分裂的培养物中是正常的。但是，Ime1蛋白的产量减少了，并且在rpl22突变细胞中Ume6阻遏物没有被破坏，从而阻止了早期减数分裂基因的诱导，从而导致了减数分裂前的I期停滞。Rpl22的这种作用不是突变不必要的大核糖体蛋白的普遍结果，因为缺乏Rpl29或Rpl39的菌株几乎以野生型效率进行减数分裂。几个结果表明Rpl22通过增强IME1 mRNA翻译起作用。首先，rpl22突变细胞中合成的Ime1蛋白表现出与野生型培养物中相同的周转率。另外，在从rpl22突变细胞分离的多核糖体部分中发现了IME1转录物，表明发生了mRNA核输出和核糖体缔合。最后，删除异常长的5'UTR可恢复rpl22突变体中的Ime1水平和减数分裂基因的早期转录，表明Rpl22可通过该元件增强翻译。多核糖体谱显示，在高翻译输出的条件下，Rp122维持高的游离60S亚基水平，从而防止半聚体形成，这是指示由未配对的40S亚基结合的mRNA的翻译物种。除减数分裂外，侵入性和假菌丝生长也需要Rpl22。结论这些发现表明，Rpl22A和Rpl22B是选择性翻译IME1 mRNA所必需的，而IME1 mRNA是减数分裂诱导和随后的配子发生所必需的。另外，我们的结果暗示Rpl22在响应环境氮信号的细胞命运开关中具有更普遍的作用。结论这些发现表明，Rpl22A和Rpl22B是选择性翻译IME1 mRNA所必需的，而IME1 mRNA是减数分裂诱导和随后的配子发生所必需的。另外，我们的结果暗示Rpl22在响应环境氮信号的细胞命运开关中具有更普遍的作用。结论这些发现表明，Rpl22A和Rpl22B是选择性翻译IME1 mRNA所必需的，而IME1 mRNA是减数分裂诱导和随后的配子发生所必需的。另外，我们的结果暗示Rpl22在响应环境氮信号的细胞命运开关中具有更普遍的作用。