Grallath Silke, Schwarz Juliane P, Böttcher Ulrike M K, Bracher Andreas, Hartl F Ulrich, Siegers Katja
Department of Cellular Biochemistry, Max Planck Institute of Biochemistry, Martinsried, Germany.
EMBO Rep. 2006 Jan;7(1):78-84. doi: 10.1038/sj.embor.7400551.
The nascent chain-associated complex (NAC) is a dimeric protein complex of archaea and eukarya that interacts with ribosomes and translating polypeptide chains. We show that, in yeast, NAC and the signal-recognition particle (SRP) share the universally conserved ribosomal protein L25 as a docking site, which is in close proximity to the ribosomal exit tunnel. The amino-terminal segment of beta-NAC was found to be required for L25 binding. Purified NAC can prevent protein aggregation in vitro and thus shows certain properties of a molecular chaperone. Interestingly, the alpha-subunit of NAC interacts with the 54 kDa subunit of SRP. Consistent with a regulatory role of NAC in protein translocation into the endoplasmic reticulum (ER), we find that deletion of NAC results in an induction of the ER stress-response pathway. These results identify L25 as a conserved interaction platform for specific cytosolic factors that guide nascent polypeptides to their proper cellular destination.
新生链相关复合体（NAC）是古细菌和真核生物中的一种二聚体蛋白质复合体，它与核糖体和正在翻译的多肽链相互作用。我们发现，在酵母中，NAC和信号识别颗粒（SRP）共享普遍保守的核糖体蛋白L25作为对接位点，该位点靠近核糖体出口通道。发现β-NAC的氨基末端片段是L25结合所必需的。纯化的NAC在体外可防止蛋白质聚集，因此显示出分子伴侣的某些特性。有趣的是，NAC的α亚基与SRP的54 kDa亚基相互作用。与NAC在蛋白质向内质网（ER）转运中的调节作用一致，我们发现缺失NAC会导致ER应激反应途径的诱导。这些结果确定L25是特定胞质因子的保守相互作用平台，这些因子将新生多肽引导至其合适的细胞目的地。
