During their maturation, nascent 40S subunits enter a translation-like quality control cycle, where they are joined by mature 60S subunits to form 80S-like ribosomes. While these assembly intermediates are essential for maturation and quality control, how they form, and how their structure promotes quality control remains unknown. To address these questions, we determined the structure of an 80S-like ribosome assembly intermediate to an overall resolution of 3.4 Å. The structure, validated by biochemical data, resolves a large body of previously paradoxical data and illustrates how assembly and translation factors cooperate to promote the formation of an interface that lacks many mature subunit contacts but is stabilized by the universally conserved Dim1. We also show how Tsr1 enables this interface by blocking the canonical binding of eIF5B to 40S subunits, while maintaining its binding to 60S. The structure also shows how this interface leads to unfolding of the platform, which allows for temporal regulation of the ATPase Fap7, thus linking 40S maturation to quality-control during ribosome assembly.

中文翻译：

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80S 前核糖体中由核糖体组装因子 Tsr1 和 Dim1 协调的开放接口能够实现 Fap7 的时间调节。

在成熟过程中，新生的 40S 亚基进入类似翻译的质量控制循环，其中它们与成熟的 60S 亚基结合形成 80S 样核糖体。虽然这些组装中间体对于成熟和质量控制至关重要，但它们如何形成以及它们的结构如何促进质量控制仍然未知。为了解决这些问题，我们确定了 80S 样核糖体组装体的结构，总体分辨率为 3.4 Å。该结构经过生化数据验证，解决了之前大量自相矛盾的数据，并说明了组装和翻译因子如何合作促进缺乏许多成熟亚基接触但由普遍保守的 Dim1 稳定的界面的形成。我们还展示了 Tsr1 如何通过阻止 eIF5B 与 40S 亚基的规范结合，同时保持其与 60S 的结合来启用此接口。该结构还显示了该界面如何导致平台展开，从而允许对 ATP 酶 Fap7 进行时间调节，从而将 40S 成熟与核糖体组装过程中的质量控制联系起来。