Ting Ya-Han, Lu Ting-Jun, Johnson Arlen W, Shie Jing-Ting, Chen Bo-Ru, Kumar S Suresh, Lo Kai-Yin
From the Department of Agricultural Chemistry, National Taiwan University, 1 Sec. 4, Roosevelt Road, Taipei 10617, Taiwan.
the Department of Molecular Biosciences, Institute for Cellular and Molecular Biology, University of Texas, Austin, Texas 78712, and.
J Biol Chem. 2017 Jan 13;292(2):585-596. doi: 10.1074/jbc.M116.747634. Epub 2016 Dec 2.
Eukaryotic ribosomes are composed of rRNAs and ribosomal proteins. Ribosomal proteins are translated in the cytoplasm and imported into the nucleus for assembly with the rRNAs. It has been shown that chaperones or karyopherins responsible for import can maintain the stability of ribosomal proteins by neutralizing unfavorable positive charges and thus facilitate their transports. Among 79 ribosomal proteins in yeast, only a few are identified with specific chaperones. Besides the classic role in maintaining protein stability, chaperones have additional roles in transport, chaperoning the assembly site, and dissociation of ribosomal proteins from karyopherins. Bcp1 has been shown to be necessary for the export of Mss4, a phosphatidylinositol 4-phosphate 5-kinase, and required for ribosome biogenesis. However, its specific function in ribosome biogenesis has not been described. Here, we show that Bcp1 dissociates Rpl23 from the karyopherins and associates with Rpl23 afterward. Loss of Bcp1 causes instability of Rpl23 and deficiency of 60S subunits. In summary, Bcp1 is a novel 60S biogenesis factor via chaperoning Rpl23 in the nucleus.
真核生物核糖体由核糖体RNA（rRNA）和核糖体蛋白组成。核糖体蛋白在细胞质中翻译，然后导入细胞核与rRNA组装。研究表明，负责导入的伴侣蛋白或核转运蛋白可以通过中和不利的正电荷来维持核糖体蛋白的稳定性，从而促进其运输。在酵母的79种核糖体蛋白中，只有少数几种被鉴定出有特定的伴侣蛋白。除了在维持蛋白质稳定性方面的经典作用外，伴侣蛋白在运输、陪伴组装位点以及使核糖体蛋白与核转运蛋白解离方面还有其他作用。已证明Bcp1是磷脂酰肌醇4-磷酸5-激酶Mss4输出所必需的，也是核糖体生物发生所必需的。然而，其在核糖体生物发生中的具体功能尚未被描述。在这里，我们表明Bcp1使Rpl23与核转运蛋白解离，然后与Rpl23结合。Bcp1的缺失导致Rpl23不稳定和60S亚基缺乏。总之，Bcp1是一种通过在细胞核中陪伴Rpl23来发挥作用的新型60S生物发生因子。
