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Nucleolar localization elements in U8 snoRNA differ from sequences required for rRNA processing
T S Lange1, A V Borovjagin, S A Gerbi
1Division of Biology and Medicine, Brown University, Providence, Rhode Island 02912, USA.
RNA (New York, N.Y.)
|July 22, 1998
Summary
Xenopus U8 small nucleolar RNA (snoRNA) localizes to nucleoli via Boxes C, D, and the Cup region, independent of rRNA processing function. These elements ensure U8 snoRNA
Area of Science:
- Molecular Biology
- Cell Biology
- Genetics
Background:
- U8 small nucleolar RNA (snoRNA) is vital for ribosomal RNA (rRNA) processing in metazoans.
- Nucleolar localization is crucial for U8 snoRNA function.
- The specific sequence and structural requirements for U8 snoRNA nucleolar localization are not fully understood.
Purpose of the Study:
- To investigate the sequence and structural elements of Xenopus U8 snoRNA necessary for its localization within the nucleolus.
- To determine if regions critical for rRNA processing are also essential for nucleolar targeting.
Main Methods:
- Injection of fluorescein-labeled wild-type and mutant Xenopus U8 snoRNA into Xenopus oocyte nuclei.
- Fluorescence microscopy to visualize U8 snoRNA localization in nucleolar preparations.
- Analysis of U8 snoRNA mutants with alterations in 5' cap, loops, stems, Boxes C and D, and the Cup region.
Main Results:
- Wild-type U8 snoRNA localized to nucleoli irrespective of its 5' cap.
- Mutations in loops or stems critical for rRNA processing did not prevent nucleolar localization.
- The spatial relationship between Boxes C and D was not essential for localization.
- The Cup region, along with Boxes C and D, acts as a nucleolar localization element (NoLE).
Conclusions:
- Nucleolar localization signals (NoLEs) in U8 snoRNA are distinct from elements required for rRNA processing.
- Boxes C, D, and the unique Cup region are key determinants of U8 snoRNA nucleolar localization.
- The Cup region may facilitate binding of proteins for nucleolar import or retention.