THE INTRINSIC ABILITY OF RIBOSOMES TO BIND TO ENDOPLASMIC-RETICULUM MEMBRANES IS REGULATED BY SIGNAL RECOGNITION PARTICLE AND NASCENT-POLYPEYTIDE-ASSOCIATED COMPLEX
THE INTRINSIC ABILITY OF RIBOSOMES TO BIND TO ENDOPLASMIC-RETICULUM MEMBRANES IS REGULATED BY SIGNAL RECOGNITION PARTICLE AND NASCENT-POLYPEYTIDE-ASSOCIATED COMPLEX
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DOI：
10.1073/pnas.92.21.9435
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发表时间：
1995-10-10
影响因子：
11.1
通讯作者：
WIEDMANN, M
中科院分区：
文献类型：
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作者：
LAURING, B;KREIBICH, G;WIEDMANN, M
信号肽引导新生多肽共翻译靶向内质网（ER）。目前认为，信号识别颗粒（SRP）通过首先与信号肽结合，然后通过将核糖体/新生链/SRP复合物引导至ER处的SRP受体来介导这种靶向。我们发现，核糖体可以通过直接结合到易位位点来介导靶向，当从胞质因子（包括SRP和新生多肽相关复合物（NAG））中纯化时，体外组装的翻译中间体代表核糖体/新生链复合物有效地结合到微粒体膜，并且它们的新生多肽随后可以有效地易位，由于从核糖体/新生链复合物中去除胞质因子也会导致无信号新生多肽的错误定位，因此我们先前研究了胞质因子如NAC和SRP的再添加是否可以恢复对靶向的保真度。在没有SRP的情况下，NAC阻止了所有含有新生链的核糖体与ER膜的结合。此外，SRP阻止NAC阻断核糖体膜协会只有当新生的多肽包含一个信号。因此，NAC是一种通过信号肽指导的SRP结合调节活性的全局核糖体结合预防因子。模型将核糖体作为靶向载体用于将新生多肽递送至易位位点。与信号肽结合，SRP和NAC通过调节与ER膜中的受体结合的核糖体膜附着位点的暴露而有助于核糖体功能的这种特异性。
Signal peptides direct the cotranslational targeting of nascent polypeptides to the endoplasmic reticulum (ER). It is currently believed that the signal recognition particle (SRP) mediates this targeting by first binding to signal peptides and then by directing the ribosome/nascent chain/SRP complex to the SRP receptor at the ER. We show that ribosomes can mediate targeting by directly binding to translocation sites, When purified away from cytosolic factors, including SRP and nascent-polypeptide-associated complex (NAG), in vitro assembled translation intermediates representing ribosome/nascent-chain complexes efficiently bound to microsomal membranes, and their nascent polypeptides could subsequently be efficiently translocated, Because removal of cytosolic factors from the ribbsome/nascent-chain complexes also resulted tn mistargeting of signalless nascent polypeptides, we previously investigated whether readdition of cytosolic factors, such as NAC and SRP, could restore fidelity to targeting. Without SRP, NAC prevented all nascent-chain-containing ribosomes from binding to the ER membrane. Furthermore, SRP prevented NAC from blocking ribosome-membrane association only when the nascent polypeptide contained a signal. Thus, NAC is a global ribosome-binding prevention factor regulated in activity by signal-peptide-directed SRP binding, A model presents ribosomes as the targeting vectors for delivering nascent polypeptides to translocation sites. In conjunction with signal peptides, SRP and NAC contribute to this specificity of ribosomal function by regulating exposure of a ribosomal membrane attachment site that binds to receptors in the ER membrane.