Jäkel S, Görlich D
Zentrum für Molekulare Biologie der Universität Heidelberg, Germany.
EMBO J. 1998 Aug 3;17(15):4491-502. doi: 10.1093/emboj/17.15.4491.
The assembly of eukaryotic ribosomal subunits takes place in the nucleolus and requires nuclear import of ribosomal proteins. We have studied this import in a mammalian system and found that the classical nuclear import pathway using the importin alpha/beta heterodimer apparently plays only a minor role. Instead, at least four importin beta-like transport receptors, namely importin beta itself, transportin, RanBP5 and RanBP7, directly bind and import ribosomal proteins. We found that the ribosomal proteins L23a, S7 and L5 can each be imported alternatively by any of the four receptors. We have studied rpL23a in detail and identified a very basic region to which each of the four import receptors bind avidly. This domain might be considered as an archetypal import signal that evolved before import receptors diverged in evolution. The presence of distinct binding sites for rpL23a and the M9 import signal in transportin, and for rpL23a and importin alpha in importin beta might explain how a single receptor can recognize very different import signals.
真核生物核糖体亚基的组装在核仁中进行，并且需要核糖体蛋白的核输入。我们在一个哺乳动物系统中研究了这种输入，发现使用输入蛋白α/β异二聚体的经典核输入途径显然只起次要作用。相反，至少有四种类输入蛋白β转运受体，即输入蛋白β本身、转运蛋白、RanBP5和RanBP7，直接结合并输入核糖体蛋白。我们发现核糖体蛋白L23a、S7和L5中的每一种都可以由这四种受体中的任何一种交替输入。我们已经详细研究了rpL23a，并确定了一个非常碱性的区域，四种输入受体中的每一种都能与之紧密结合。这个结构域可能被认为是一种原型输入信号，它在进化过程中输入受体分化之前就已经进化出来了。转运蛋白中存在针对rpL23a和M9输入信号的不同结合位点，以及输入蛋白β中存在针对rpL23a和输入蛋白α的结合位点，这可能解释了单个受体如何能够识别非常不同的输入信号。
