In eukaryotes, the beak structure of 40S subunits is formed by the protrusion of the 18S rRNA helix 33 and three ribosomal proteins: eS10, eS12 and eS31. The exact role of these proteins in ribosome biogenesis is not well understood. While eS10 is an essential protein encoded by two paralogous genes in Saccharomyces cerevisiae, eS12 and eS31 are not essential proteins encoded by the single-copy genes RPS12 and UBI3, respectively. Here, we have analysed the contribution of yeast eS12 to ribosome biogenesis and compared it with that of eS31. Polysome analysis reveals that deletion of either RPS12 or UBI3 results in equivalent 40S deficits. Analysis of pre-rRNA processing indicates that eS12, akin to eS31, is required for efficient processing of 20S pre-rRNA to mature 18S rRNA. Moreover, we show that the 20S pre-rRNA accumulates within cytoplasmic pre-40S particles, as deduced from FISH experiments and the lack of nuclear retention of 40S subunit reporter proteins, in rps12∆ and ubi3∆ cells. However, these particles containing 20S pre-rRNA are not efficiently incorporated into polyribosomes. We also provide evidence for a genetic interaction between eS12 or eS31 and the late-acting 40S assembly factors Enp1 and Ltv1, which appears not to be linked to the dynamics of their association with or release from pre-40S particles in the absence of either eS12 or eS31. Finally, we show that eS12- and eS31-deficient ribosomes exhibit increased levels of translational misreading. Altogether, our data highlight distinct important roles of the beak region during ribosome assembly and function.

在真核生物中，40S亚基的喙结构由18S rRNA螺旋33和三种核糖体蛋白（eS10，eS12和eS31）的突出部分形成。这些蛋白质在核糖体生物发生中的确切作用尚不清楚。尽管eS10是由酿酒酵母中两个旁系同源基因编码的必需蛋白，但是eS12和eS31分别不是由单拷贝基因RPS12和UBI3编码的必需蛋白。在这里，我们分析了酵母eS12对核糖体生物发生的贡献，并将其与eS31进行了比较。多核糖体分析显示RPS12或UBI3的缺失导致等效的40S赤字。前rRNA加工的分析表明，类似于eS31的eS12是有效地将20S前rRNA加工成成熟的18S rRNA所必需的。此外，我们证明了20S pre-rRNA会在rps12∆和ubi3∆中的FISH实验和40S亚基报道蛋白缺乏核保留的情况下，在40S前质颗粒中积累。细胞。但是，这些含有20S pre-rRNA的颗粒不能有效地掺入多核糖体中。我们还为eS12或eS31与40S后期组装因子Enp1和Ltv1之间的遗传相互作用提供了证据，在没有eS12的情况下，这似乎与它们与40S之前的颗粒缔合或释放的动力学无关。或eS31。最后，我们显示eS12和eS31缺陷核糖体表现出水平的翻译误读。总之，我们的数据突出了喙区域在核糖体组装和功能过程中的不同重要作用。