Escherichia coli YaeJ protein mediates a novel ribosome-rescue pathway distinct from SsrA- and ArfA-mediated pathways
Escherichia coli YaeJ protein mediates a novel ribosome-rescue pathway distinct from SsrA- and ArfA-mediated pathways
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DOI：
10.1111/j.1365-2958.2011.07607.x
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发表时间：
2011-05-01
影响因子：
3.6
通讯作者：
Abo, Tatsuhiko
中科院分区：
文献类型：
--
作者：
Chadani, Yuhei;Ono, Katsuhiko;Abo, Tatsuhiko
在没有终止密码子的mRNA（非终止mRNA）的3'末端停滞的核糖体的积累被认为对细菌细胞是有毒的。大肠杆菌至少有两种不同的系统来拯救这种停滞的核糖体：SsrA依赖的反式翻译和ArfA依赖的核糖体拯救。ssrA和arfA突变的组合是合成致死的，表明核糖体拯救的意义。在这项研究中，我们确定了E。coli yaeJ基因，编码一个GGQ基序的肽释放因子同源物，是ssrA arfA双突变体致死表型的多拷贝抑制因子。YaeJ蛋白被证明与核糖体结合。无论在体内还是体外，YaeJ都表现出核糖体拯救活性，并促进停滞核糖体中肽基tRNA的水解。GGQ基序中的错义突变或C-末端非结构化尾部的缺失废除了ssrA arfA合成致死性和核糖体拯救活性的抑制活性，表明这些结构特征的重要性。基于这些观察结果，我们提出YaeJ通过与停滞在非终止mRNA的3'末端的核糖体结合而充当终止密码子非依赖性肽基-tRNA水解因子。还表明ArfA和YaeJ通过不同的机制拯救停滞的核糖体。
P>Accumulation of stalled ribosomes at the 3' end of mRNA without a stop codon (non-stop mRNA) is supposed to be toxic to bacterial cells. Escherichia coli has at least two distinct systems to rescue such stalled ribosomes: SsrA-dependent trans-translation and ArfA-dependent ribosome rescue. Combination of the ssrA and arfA mutations is synthetically lethal, suggesting the significance of ribosome rescue. In this study, we identified the E. coli yaeJ gene, encoding a peptide-release factor homologue with GGQ motif, as a multicopy suppressor of the lethal phenotype of ssrA arfA double mutant. The YaeJ protein was shown to bind to ribosomes. Both in vivo and in vitro, YaeJ showed the ribosome-rescue activity and promoted the hydrolysis of peptidyl-tRNA residing in the stalled ribosome. Missense mutation in the GGQ motif or deletion of the C-terminal unstructured tail abolished both the suppressor activity for ssrA arfA synthetic lethality and the ribosome-rescue activity, suggesting the importance of these structural features. On the basis of these observations, we propose that YaeJ acts as a stop codon-independent peptidyl-tRNA hydrolysing factor through binding to ribosomes stalled at the 3' end of non-stop mRNAs. It was also suggested that ArfA and YaeJ rescue the stalled ribosomes by distinct mechanisms.