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Updated: Aug 4, 2026
Isolation of Cognate RNA-protein Complexes from Cells Using Oligonucleotide-directed Elution
Published on: January 16, 2017
Basic domains target protein subunits of the RNase MRP complex to the nucleolus independently of complex association
H van Eenennaam1, A van der Heijden, R J Janssen
1Department of Biochemistry, University of Nijmegen, NL-6500 HB Nijmegen, The Netherlands.
Abstract:
The RNase MRP and RNase P ribonucleoprotein particles both function as endoribonucleases, have a similar RNA component, and share several protein subunits. RNase MRP has been implicated in pre-rRNA processing and mitochondrial DNA replication, whereas RNase P functions in pre-tRNA processing. Both RNase MRP and RNase P accumulate in the nucleolus of eukaryotic cells. In this report we show that for three protein subunits of the RNase MRP complex (hPop1, hPop4, and Rpp38) basic domains are responsible for their nucleolar accumulation and that they are able to accumulate in the nucleolus independently of their association with the RNase MRP and RNase P complexes. We also show that certain mutants of hPop4 accumulate in the Cajal bodies, suggesting that hPop4 traverses through these bodies to the nucleolus. Furthermore, we characterized a deletion mutant of Rpp38 that preferentially associates with the RNase MRP complex, giving a first clue about the difference in protein composition of the human RNase MRP and RNase P complexes. On the basis of all available data on nucleolar localization sequences, we hypothesize that nucleolar accumulation of proteins containing basic domains proceeds by diffusion and retention rather than by an active transport process. The existence of nucleolar localization sequences is discussed.
Insights
Basic domains on RNase MRP and RNase P protein subunits, like hPop1, hPop4, and Rpp38, drive their nucleolar accumulation. This suggests proteins move to the nucleolus via diffusion and retention.
Area of Science:
- Molecular Biology
- Cell Biology
- Biochemistry
Background:
- RNase MRP and RNase P are ribonucleoprotein endoribonucleases with shared RNA and protein components.
- RNase MRP is involved in pre-rRNA processing and mitochondrial DNA replication.
- RNase P is essential for pre-tRNA processing.
- Both complexes localize to the nucleolus in eukaryotic cells.
Purpose of the Study:
- To investigate the role of basic domains in the nucleolar accumulation of RNase MRP subunits.
- To determine if nucleolar accumulation is dependent on complex association.
- To explore the pathway of protein trafficking to the nucleolus.
Main Methods:
- Analysis of protein subunit localization using mutant constructs.
- Characterization of deletion mutants for complex association.
- Investigation of nucleolar localization sequences (NLSs).
Main Results:
- Basic domains in hPop1, hPop4, and Rpp38 mediate independent nucleolar accumulation.
- Mutant hPop4 variants accumulate in Cajal bodies, suggesting a trafficking route.
- A specific Rpp38 deletion mutant favors RNase MRP association, hinting at compositional differences.
Conclusions:
- Nucleolar accumulation of proteins with basic domains likely occurs via diffusion and retention, not active transport.
- Basic domains function as nucleolar localization sequences.
- Findings provide insights into the distinct protein compositions of human RNase MRP and RNase P.
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