An Extensive Network of Information Flow through the B1b/c Intersubunit Bridge of the Yeast Ribosome

Yeast ribosomal proteins L11 and S18 form a dynamic intersubunit interaction called the B1b/c bridge. Recent high resolution images of the ribosome have enabled targeting of specific residues in this bridge to address how distantly separated regions within the large and small subunits of the ribosome communicate with each other. Mutations were generated in the L11 side of the B1b/c bridge with a particular focus on disrupting the opposing charge motifs that have previously been proposed to be involved in subunit ratcheting. Mutants had wide-ranging effects on cellular viability and translational fidelity, with the most pronounced phenotypes corresponding to amino acid changes resulting in alterations of local charge properties. Chemical protection studies of selected mutants revealed rRNA structural changes in both the large and small subunits. In the large subunit rRNA, structural changes mapped to Helices 39, 80, 82, 83, 84, and the peptidyltransferase center. In the small subunit rRNA, structural changes were identified in helices 30 and 42, located between S18 and the decoding center. The rRNA structural changes correlated with charge-specific alterations to the L11 side of the B1b/c bridge. These analyses underscore the importance of the opposing charge mechanism in mediating B1b/c bridge interactions and suggest an extensive network of information exchange between distinct regions of the large and small subunits.

酵母核糖体蛋白L11（Yeast ribosomal protein L11）与S18可形成一种动态的亚基间相互作用，即B1b/c桥（B1b/c bridge）。近期核糖体的高分辨率结构解析图像，使得研究人员能够靶向B1b/c桥内的特定残基，以探究核糖体大亚基与小亚基内相距较远的区域之间的通信机制。研究团队在B1b/c桥的L11侧引入突变，重点破坏此前被认为参与亚基棘轮运动（subunit ratcheting）的反向电荷基序。这些突变体对细胞活力与翻译保真度产生了广泛影响，其中表型最为显著的是导致局部电荷性质改变的氨基酸突变。对选定突变体开展的化学保护实验显示，大亚基与小亚基内均出现核糖体RNA（rRNA, ribosomal RNA）结构变化。在大亚基rRNA中，结构变化定位至螺旋39、80、82、83、84以及肽酰转移酶中心（peptidyltransferase center）；在小亚基rRNA中，结构变化出现在位于S18与解码中心（decoding center）之间的螺旋30和42。rRNA结构变化与B1b/c桥L11侧的电荷特异性改变密切相关。上述分析强调了反向电荷机制在介导B1b/c桥相互作用中的重要性，并表明核糖体大亚基与小亚基的不同区域之间存在广泛的信息交换网络。