U8 小核仁 RNA 中的核仁定位元件与核糖体 RNA 加工所需的序列不同。
Nucleolar localization elements in U8 snoRNA differ from sequences required for rRNA processing.
作者信息
Lange T S, Borovjagin A V, Gerbi S A
机构信息
Division of Biology and Medicine, Brown University, Providence, Rhode Island 02912, USA.
出版信息
RNA. 1998 Jul;4(7):789-800. doi: 10.1017/s1355838298980438.
U8 small nucleolar RNA (snoRNA) is essential for metazoan ribosomal RNA (rRNA) processing in nucleoli. The sequences and structural features in Xenopus U8 snoRNA that are required for its nucleolar localization were analyzed. Fluorescein-labeled U8 snoRNA was injected into Xenopus oocyte nuclei, and fluorescence microscopy of nucleolar preparations revealed that wild-type Xenopus U8 snoRNA localized to nucleoli, regardless of the presence or nature of the 5' cap on the injected U8 snoRNA. Nucleolar localization was observed when loops or stems in the 5' portion of U8 that are critical for U8 snoRNA function in rRNA processing were mutated. Therefore, sites of interaction in U8 snoRNA that potentially tether it to pre-rRNA are not essential for nucleolar localization of U8. Boxes C and D are known to be nucleolar localization elements (NoLEs) for U8 snoRNA and other snoRNAs of the Box C/D family. However, the spatial relationship of Box C to Box D was not crucial for U8 nucleolar localization, as demonstrated here by deletion of sequences in the two stems that separate them. These U8 mutants can localize to nucleoli and function in rRNA processing as well. The single-stranded Cup region in U8, adjacent to evolutionarily conserved Box C, functions as a NoLE in addition to Boxes C and D. Cup is unique to U8 snoRNA and may help bind putative protein(s) needed for nucleolar localization. Alternatively, Cup may help to retain U8 snoRNA within the nucleolus.
U8小核仁RNA（snoRNA）对于后生动物核仁中核糖体RNA（rRNA）的加工至关重要。分析了非洲爪蟾U8 snoRNA核仁定位所需的序列和结构特征。将荧光素标记的U8 snoRNA注射到非洲爪蟾卵母细胞核中，对核仁制剂进行荧光显微镜观察发现，无论注射的U8 snoRNA上5'帽的存在与否或性质如何，野生型非洲爪蟾U8 snoRNA都定位于核仁。当U8 5'部分对rRNA加工中U8 snoRNA功能至关重要的环或茎发生突变时，仍可观察到核仁定位。因此，U8 snoRNA中可能将其与前体rRNA相连的相互作用位点对于U8的核仁定位并非必不可少。已知C盒和D盒是U8 snoRNA以及C/D盒家族其他snoRNA的核仁定位元件（NoLEs）。然而，如本文通过缺失分隔它们的两个茎中的序列所证明的，C盒与D盒的空间关系对于U8核仁定位并不关键。这些U8突变体也可以定位于核仁并在rRNA加工中发挥作用。U8中与进化保守的C盒相邻的单链Cup区域，除了C盒和D盒外，还作为一个NoLE发挥作用。Cup是U8 snoRNA特有的，可能有助于结合核仁定位所需的假定蛋白质。或者，Cup可能有助于将U8 snoRNA保留在核仁内。
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