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Signal recognition particle components in the nucleolus.
J C Politz1, S Yarovoi, S M Kilroy
1Department of Biochemistry, University of Massachusetts Medical School, 377 Plantation Street, Suite 337, Worcester, MA 01605, USA.
Summary
Signal recognition particle (SRP) components, including SRP RNA, SRP19, SRP68, and SRP72, localize to the nucleolus. This suggests partial SRP assembly occurs in the nucleolus, a novel finding for this ribonucleoprotein complex.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- The signal recognition particle (SRP) is crucial for targeting proteins to the endoplasmic reticulum (ER).
- Recent findings indicate SRP RNA is present in the nucleolus, suggesting a broader role for this organelle.
- The localization of other SRP components within the nucleolus remained unexplored.
Purpose of the Study:
- To investigate the nucleolar localization of SRP components.
- To determine if the nucleolus serves as a site for SRP assembly or other functions.
Main Methods:
- Transfection of rat fibroblasts with green fluorescent protein (GFP) fusions of SRP proteins.
- Immunofluorescence microscopy to detect protein localization.
- In situ hybridization to detect endogenous SRP RNA.
Main Results:
- GFP-fusions of SRP19, SRP68, and SRP72 localized to the nucleolus and cytoplasm.
- SRP68 also localized to the ER.
- SRP54 was detected in the cytoplasm but not the nucleolus.
- Endogenous SRP RNA was found in the nucleolus.
Conclusions:
- SRP RNA and three SRP proteins (SRP19, SRP68, SRP72) localize to the nucleolus.
- This suggests partial SRP assembly or other SRP-related activities occur in the nucleolus.
- SRP54 appears to interact with SRP post-nucleolar, aligning with in vitro assembly data.