Wakabayashi Hironao, Zhu Mingyi, Grayhack Elizabeth J, Mathews David H, Ermolenko Dmitri N
University of Rochester Medical Center.
University of Rochester Medical Center
RNA. 2025 Jul 31. doi: 10.1261/rna.080493.125.
During eukaryotic translation initiation, the small (40S) ribosomal subunit is recruited to the 5' cap and subsequently scans the 5' untranslated region (5' UTR) of mRNA in search of the start codon. The molecular mechanism of mRNA scanning remains unclear, particularly the requirement for and identity of a translocase. Here, using GFP reporters in Saccharomyces cerevisiae, we show that order-of-magnitude variations in the length of unstructured 5' UTRs have only modest effects on protein synthesis, while structured 5' UTRs strongly inhibit translation. Thus, when not hindered by secondary structure, mRNA scanning is not rate limiting. Loss-of-function mutations in eIF4A, Ded1 and Slh1 reveal that these translational helicases are dispensable for mRNA scanning. Our data suggest that one-dimensional diffusion predominately enables 40S movement along the 5' UTR during mRNA scanning.
在真核生物翻译起始过程中，小（40S）核糖体亚基被招募到5'帽，随后扫描mRNA的5'非翻译区（5'UTR）以寻找起始密码子。mRNA扫描的分子机制仍不清楚，特别是转位酶的需求和特性。在这里，我们利用酿酒酵母中的绿色荧光蛋白（GFP）报告基因表明，无结构的5'UTR长度在数量级上的变化对蛋白质合成只有适度影响，而有结构的5'UTR则强烈抑制翻译。因此，当不受二级结构阻碍时，mRNA扫描不是限速步骤。eIF4A、Ded1和Slh1的功能丧失突变表明，这些翻译解旋酶对于mRNA扫描是可有可无的。我们的数据表明，在mRNA扫描过程中，一维扩散主要使40S沿着5'UTR移动。
