A dual role of the ribosome-bound chaperones RAC/Ssb in maintaining the fidelity of translation termination
A dual role of the ribosome-bound chaperones RAC/Ssb in maintaining the fidelity of translation termination
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DOI：
10.1093/nar/gkz334
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发表时间：
2019-07-26
影响因子：
14.9
通讯作者：
Rospert, Sabine
中科院分区：
文献类型：
--
作者：
Gribling-Burrer, Anne-Sophie;Chiabudini, Marco;Rospert, Sabine
酵母核糖体相关复合物RAC和Hsp 70同源物Ssb锚定到核糖体上，并一起充当新生多肽折叠和共翻译组装的分子伴侣。此外，RAC/Ssb系统在保持翻译终止的保真度方面起着至关重要的作用;然而，后者的功能知之甚少。在这里，我们表明，RAC/SSB系统通过两种不同的机制，促进翻译终止的保真度。首先，通过与核糖体和新生链的直接接触，RAC/Ssb促进编码聚赖氨酸片段的易失速的聚-AAG/A序列的翻译。该功能的损害导致核糖体停滞增强和在AAG/A密码子处过早的新生多肽释放。第二，RAC/Ssb是组装全功能核糖体所必需的。当RAC/Ssb不存在时，核糖体生物合成受到阻碍，使得核心核糖体颗粒在解码和肽基转移酶中心处发生结构改变。因此，在RAC/Ssb的情况下组装的核糖体以高亲和力（K-D = 76.6 nM）与氨基糖苷巴龙霉素结合，并显示终止密码子和有义密码子之间的辨别力受损。结合的数据揭示了RAC/Ssb系统促进新合成多肽的不受阻碍的生物合成的多种机制。
The yeast ribosome-associated complex RAC and the Hsp70 homolog Ssb are anchored to the ribosome and together act as chaperones for the folding and co-translational assembly of nascent polypeptides. In addition, the RAC/Ssb system plays a crucial role in maintaining the fidelity of translation termination; however, the latter function is poorly understood. Here we show that the RAC/Ssb system promotes the fidelity of translation termination via two distinct mechanisms. First, via direct contacts with the ribosome and the nascent chain, RAC/Ssb facilitates the translation of stalling-prone poly-AAG/A sequences encoding for polylysine segments. Impairment of this function leads to enhanced ribosome stalling and to premature nascent polypeptide release at AAG/A codons. Second, RAC/Ssb is required for the assembly of fully functional ribosomes. When RAC/Ssb is absent, ribosome biogenesis is hampered such that core ribosomal particles are structurally altered at the decoding and peptidyl transferase centers. As a result, ribosomes assembled in the absence of RAC/Ssb bind to the aminoglycoside paromomycin with high affinity (K-D = 76.6 nM) and display impaired discrimination between stop codons and sense codons. The combined data shed light on the multiple mechanisms by which the RAC/Ssb system promotes unimpeded biogenesis of newly synthesized polypeptides.