Ginisty H, Amalric F, Bouvet P
Laboratoire de Biologie Moléculaire Eucaryote, Institut de Biologie Cellulaire et de Génétique du CNRS, UPR 9006, 118 route de Narbonne, 31062 Toulouse Cedex, France.
EMBO J. 1998 Mar 2;17(5):1476-86. doi: 10.1093/emboj/17.5.1476.
The first processing step of precursor ribosomal RNA (pre-rRNA) involves a cleavage within the 5' external transcribed spacer. This processing requires sequences downstream of the cleavage site which are perfectly conserved among human, mouse and Xenopus and also several small nucleolar RNAs (snoRNAs): U3, U14, U17 and E3. In this study, we show that nucleolin, one of the major RNA-binding proteins of the nucleolus, is involved in the early cleavage of pre-rRNA. Nucleolin interacts with the pre-rRNA substrate, and we demonstrate that this interaction is required for the processing reaction in vitro. Furthermore, we show that nucleolin interacts with the U3 snoRNP. Increased levels of nucleolin, in the presence of the U3 snoRNA, activate the processing activity of a S100 cell extract. Our results suggest that the interaction of nucleolin with the pre-rRNA substrate might be a limiting step in the primary processing reaction. Nucleolin is the first identified metazoan proteinaceous factor that interacts directly with the rRNA substrate and that is required for the processing reaction. Potential roles for nucleolin in the primary processing reaction and in ribosome biogenesis are discussed.
前体核糖体RNA（pre-rRNA）的首个加工步骤涉及5'外部转录间隔区的切割。该加工过程需要切割位点下游的序列，这些序列在人类、小鼠和非洲爪蟾中完全保守，还需要几种小核仁RNA（snoRNA）：U3、U14、U17和E3。在本研究中，我们表明核仁素是核仁中主要的RNA结合蛋白之一，参与pre-rRNA的早期切割。核仁素与pre-rRNA底物相互作用，并且我们证明这种相互作用在体外加工反应中是必需的。此外，我们表明核仁素与U3 snoRNP相互作用。在U3 snoRNA存在的情况下，核仁素水平的升高会激活S100细胞提取物的加工活性。我们的结果表明，核仁素与pre-rRNA底物的相互作用可能是初级加工反应中的一个限制步骤。核仁素是首个被鉴定出的后生动物蛋白质因子，它直接与rRNA底物相互作用且是加工反应所必需的。文中讨论了核仁素在初级加工反应和核糖体生物发生中的潜在作用。
