Related Experiment Video
Updated: Jun 12, 2026
07:26
Discrimintion and Mapping of the Primary and Processed Transcripts in Maize Mitochondrion Using a Circular RT-PCR-based Strategy
Published on: July 29, 2019
Expression of four mitochondrial tRNAs from only two loci.
Jessica M Warren1,2, Kasavajhala V S K Prasad3, Anistynn M Mendez1
1Biodesign Institute and School of Life Sciences, Arizona State University, Tempe, AZ 85281.
Summary
Mitochondria use "mirror" transfer RNAs (tRNAs) from a single gene locus to decode two amino acids. This discovery reveals a novel strategy for maintaining essential mitochondrial tRNAs during extensive gene loss.
Area of Science:
- Mitochondrial biology
- Molecular evolution
- RNA biology
Background:
- Animal mitochondrial genomes retain few genes, including transfer RNAs (tRNAs), from bacterial ancestors.
- Mitochondrial tRNAs (mt-tRNAs) are often structurally aberrant and can be truncated, challenging definitions of functional tRNAs.
Purpose of the Study:
- To investigate novel tRNA gene architectures in animal mitochondria.
- To characterize a unique "mirror" tRNA pair produced from opposite strands of the same locus.
Main Methods:
- Analysis of mitochondrial genome architecture.
- Biochemical assays to confirm aminoacylation of mirror tRNAs.
- Localization studies within mitoribosomes.
- Investigation of posttranscriptional modifications and RNA editing.
Main Results:
- Identified two overlapping "mirror" tRNAs transcribed from opposite strands of a single locus.
- Demonstrated that these mirror tRNAs are aminoacylated and functional within mitoribosomes.
- Observed strand-specific nucleotide modifications and RNA editing on mirror tRNAs, dependent on transcriptional orientation.
Conclusions:
- Mirror tRNAs represent a novel mechanism for maintaining a complete tRNA set in compact mitochondrial genomes.
- This bidirectional gene expression strategy has significant implications for the evolution of tRNA genes, mitochondrial function, and the origins of protein synthesis.
Related Concept Videos
02:59Animal Mitochondrial Genetics
Among all the organelles in an animal cell, only mitochondria have their own independent genomes. Animal mitochondrial DNA is a double-stranded, closed-circular molecule with around 20,000 base pairs. Mitochondrial DNA is unique in that one of its two strands, the heavy, or H, -strand is guanine rich, whereas the complementary strand is cytosine rich and called the light, or L, -strand. Compared to nuclear DNA, mitochondrial DNA has a very low percentage of non-coding regions and is marked by...
01:39Mitochondrial Protein Sorting
Mitochondria are double-membrane organelles of the eukaryotes involved in cellular metabolism, signaling, ATP synthesis, and programmed cell death. Each of these processes requires specific proteins and enzymes that must be correctly sorted to the right mitochondrial subcompartment for the proper functioning of the organelle.
Most of these mitochondrial proteins are encoded by the nucleus and imported to the mitochondria as unfolded or loosely folded precursors. Mitochondrial precursors...
Most of these mitochondrial proteins are encoded by the nucleus and imported to the mitochondria as unfolded or loosely folded precursors. Mitochondrial precursors...
02:19Export of Mitochondrial and Chloroplast Genes
A eukaryotic cell can have up to three different types of genetic systems: nuclear, mitochondrial, and chloroplast. During evolution, organelles have exported many genes to the nucleus; this transfer is still ongoing in some plant species. Approximately 18% of the Arabidopsis thaliana nuclear genome is thought to be derived from the chloroplast’s cyanobacterial ancestor, and around 75% of the yeast genome derived from the mitochondria’s bacterial ancestor. This export has occurred irrespective...
01:34Protein Transport into the Inner Mitochondrial Membrane
Nuclear encoded mitochondrial precursors are imported to the inner membrane in a multistep process involving two separate translocons, TIM22 and TIM23. TIM23 is a cation-selective pore that remains closed by the N terminal segment of the protein. Negative charges on the TIM23 act as a receptor for the incoming precursor, pulling the positively charged matrix-targeting sequence for peptide insertion and translocation.
Transport of mitochondrial precursors across the TIM23 channel is driven by...
Transport of mitochondrial precursors across the TIM23 channel is driven by...
01:19Translocation of Proteins into the Mitochondria
Mitochondrial precursors are translocated to the internal subcompartments via independent mechanisms involving distinct protein machineries called translocases.
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,...
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,...
02:16Comparing Mitochondrial, Chloroplast, and Prokaryotic Genomes
The present-day mitochondrial and chloroplast genomes have retained some of the characteristics of their ancestral prokaryotes and also have acquired new attributes during their evolution within eukaryotic cells. Like prokaryotic genomes, mitochondrial and chloroplast genomes neither bind with histone-like proteins nor show complex packaging into chromosome-like structures, as observed in eukaryotes. Unlike mitotic cell divisions observed in eukaryotic cells, mitochondria and chloroplasts...