Related Experiment Video
Updated: Mar 30, 2026
Rapid Isolation of the Mitoribosome from HEK Cells
Published on: October 4, 2018
Mitochondrial Ribosomal Protein L12 Is Required for POLRMT Stability and Exists as Two Forms Generated by Alternative
Jessica Nouws1, Arvind V Goswami1, Megan Bestwick2
1From the Departments of Pathology and.
Abstract:
To translate the 13 mtDNA-encoded mRNAs involved in oxidative phosphorylation (OXPHOS), mammalian mitochondria contain a dedicated set of ribosomes comprising rRNAs encoded by the mitochondrial genome and mitochondrial ribosomal proteins (MRPs) that are encoded by nuclear genes and imported into the matrix. In addition to their role in the ribosome, several MRPs have auxiliary functions or have been implicated in other cellular processes like cell cycle regulation and apoptosis. For example, we have shown that human MRPL12 binds and activates mitochondrial RNA polymerase (POLRMT), and hence has distinct functions in the ribosome and mtDNA transcription. Here we provide concrete evidence that there are two mature forms of mammalian MRPL12 that are generated by a two-step cleavage during import, involving efficient cleavage by mitochondrial processing protease and a second inefficient or regulated cleavage by mitochondrial intermediate protease. We also show that knock-down of MRPL12 by RNAi results in instability of POLRMT, but not other primary mitochondrial transcription components, and a corresponding decrease in mitochondrial transcription rates. Knock-down of MRPL10, the binding partner of MRPL12 in the ribosome, results in selective degradation of the mature long form of MRPL12, but has no effect on POLRMT. We propose that the two forms of MRPL12 are involved in homeostatic regulation of mitochondrial transcription and ribosome biogenesis that likely contribute to cell cycle, growth regulation, and longevity pathways to which MRPL12 has been linked.
Insights
Mammalian mitochondria utilize two forms of mitochondrial ribosomal protein L12 (MRPL12) for regulating mitochondrial transcription and ribosome biogenesis. These forms are crucial for maintaining mitochondrial gene expression and cellular processes like growth and longevity.
Area of Science:
- Mitochondrial biology
- Molecular genetics
- Cellular respiration
Background:
- Mitochondria rely on mitochondrial ribosomes (MRPs) for translating 13 mtDNA-encoded mRNAs essential for oxidative phosphorylation (OXPHOS).
- Mitochondrial ribosomal proteins (MRPs) possess functions beyond ribosome assembly, including roles in mtDNA transcription, cell cycle, and apoptosis.
- Human MRPL12 is known to bind and activate mitochondrial RNA polymerase (POLRMT), indicating dual roles in ribosome function and mtDNA transcription.
Purpose of the Study:
- To investigate the existence and function of distinct mature forms of mammalian MRPL12.
- To elucidate the processing pathway and regulatory mechanisms of MRPL12.
- To determine the impact of MRPL12 and its binding partner MRPL10 on mitochondrial transcription and ribosome biogenesis.
Main Methods:
- Analysis of MRPL12 processing via two-step cleavage involving mitochondrial processing protease and mitochondrial intermediate protease.
- RNA interference (RNAi) to knock down MRPL12 and MRPL10 expression.
- Assessment of POLRMT stability and mitochondrial transcription rates following knock-down experiments.
Main Results:
- Two mature forms of mammalian MRPL12 are generated through a sequential cleavage process during mitochondrial import.
- Knock-down of MRPL12 leads to POLRMT instability and reduced mitochondrial transcription rates.
- Knock-down of MRPL10 selectively degrades the long form of MRPL12 without affecting POLRMT.
Conclusions:
- The two forms of MRPL12 play a critical role in the homeostatic regulation of mitochondrial transcription and ribosome biogenesis.
- MRPL12's dual forms likely contribute to cellular processes including cell cycle, growth regulation, and longevity.
- MRPL10 influences MRPL12 processing, highlighting coordinated regulation within mitochondrial protein synthesis and transcription machinery.
More Related Videos
Related Concept Videos
01:39Mitochondrial Precursor Proteins
Most of the mitochondrial...
01:39Mitochondrial Protein Sorting
Most of these mitochondrial proteins are encoded by the nucleus and imported to the mitochondria as unfolded or loosely folded precursors. Mitochondrial precursors...
01:19Translocation of Proteins into the Mitochondria
Sorting of outer membrane proteins:
Mitochondrial outer membrane proteins are of two types: the transmembrane, beta-barrel porins, and the membrane-anchored, alpha-helical proteins. Beta-barrel porin precursors are translocated by the TOM complex and inserted into the outer mitochondrial membrane by the SAM complex. In contrast,...
02:53Ribosomal RNA Synthesis
Ribosome biogenesis begins with the synthesis of 5S and 45S pre-rRNAs by distinct RNA polymerases. The primary transcripts are extensively processed and modified before they are bound and folded by ribosomal proteins and assembly factors,...
02:53Ribosomal RNA Synthesis
01:12Porin Insertion in the Outer Mitochondrial Membrane
Three models describe the assembly of porins by the SAM complex and their insertion into the outer membrane. Model 1 suggests that porins are assembled outside the SAM channel as the...