Politz Joan C, Lewandowski Laura B, Pederson Thoru
Department of Biochemistry and Molecular Pharmacology, Program in Cell Dynamics, University of Massachusetts Medical School, 377 Plantation Street, Worcester, MA 01605, USA.
J Cell Biol. 2002 Nov 11;159(3):411-8. doi: 10.1083/jcb.200208037.
The nucleolus is the site of ribosome biosynthesis, but is now known to have other functions as well. In the present study we have investigated how the distribution of signal recognition particle (SRP) RNA within the nucleolus relates to the known sites of ribosomal RNA synthesis, processing, and nascent ribosome assembly (i.e., the fibrillar centers, the dense fibrillar component (DFC), and the granular component). Very little SRP RNA was detected in fibrillar centers or the DFC of the nucleolus, as defined by the RNA polymerase I-specific upstream binding factor and the protein fibrillarin, respectively. Some SRP RNA was present in the granular component, as marked by the protein B23, indicating a possible interaction with ribosomal subunits at a later stage of maturation. However, a substantial portion of SRP RNA was also detected in regions of the nucleolus where neither B23, UBF, or fibrillarin were concentrated. Dual probe in situ hybridization experiments confirmed that a significant fraction of nucleolar SRP RNA was not spatially coincident with 28S ribosomal RNA. These results demonstrate that SRP RNA concentrates in an intranucleolar location other than the classical stations of ribosome biosynthesis, suggesting that there may be nucleolar regions that are specialized for other functions.
核仁是核糖体生物合成的场所，但现在已知它也具有其他功能。在本研究中，我们研究了核仁内信号识别颗粒（SRP）RNA的分布与核糖体RNA合成、加工及新生核糖体组装的已知位点（即纤维中心、致密纤维组分（DFC）和颗粒组分）之间的关系。分别由RNA聚合酶I特异性上游结合因子和蛋白质纤维蛋白原定义的核仁纤维中心或DFC中，检测到的SRP RNA极少。蛋白质B23标记显示，颗粒组分中存在一些SRP RNA，表明在成熟后期它可能与核糖体亚基相互作用。然而，在核仁中B23、上游结合因子（UBF）或纤维蛋白原均未富集的区域也检测到相当一部分SRP RNA。双探针原位杂交实验证实，相当一部分核仁SRP RNA在空间上与28S核糖体RNA不重合。这些结果表明，SRP RNA集中在核糖体生物合成经典位点以外的核仁内位置，这表明可能存在专门用于其他功能的核仁区域。
