ABSTRACT
Mitochondria play a key role in essential cellular functions. A deeper understanding of mitochondrial molecular processes is hampered by the difficulty of incorporating foreign nucleic acids into organelles. Mitochondria of most eukaryotic species import cytosolic tRNAs. Based on this natural process, we describe here a powerful shuttle system to internalize several types of RNAs into isolated mitochondria. We demonstrate that this tool is useful to investigate tRNA processing or mRNA editing in plant mitochondria. Furthermore, we show that the same strategy can be used to address both tRNA and mRNA to isolated mammalian mitochondria. We anticipate our novel approach to be the starting point for various studies on mitochondrial processes. Finally, our study provides new insights into the mechanism of RNA import into mitochondria.
Subject(s)
Mitochondria/metabolism , Nucleobase, Nucleoside, Nucleotide, and Nucleic Acid Transport Proteins/metabolism , RNA Transport , Base Sequence , Larix/genetics , Mitochondrial Proton-Translocating ATPases/metabolism , Molecular Sequence Data , RNA Editing , RNA Precursors/chemistry , RNA Precursors/metabolism , RNA Processing, Post-Transcriptional , RNA, Messenger/metabolism , RNA, Transfer/metabolism , RNA, Transfer, His/chemistry , RNA, Transfer, His/metabolism , Solanum tuberosum/metabolism , Tetrahydrofolate Dehydrogenase/metabolismABSTRACT
Mitochondria, owing to their bacterial origin, still contain their own DNA. However, the majority of bacterial genes were lost or transferred to the nuclear genome and the biogenesis of the "present-day" mitochondria mainly depends on the expression of the nuclear genome. Thus, most mitochondrial proteins and a small number of mitochondrial RNAs (mostly tRNAs) expressed from nuclear genes need to be imported into the organelle. During evolution, macromolecule import systems were universally established. The processes of protein mitochondrial import are very well described in the literature. By contrast, deciphering the mitochondrial RNA import phenomenon is still a real challenge. The purpose of this review is to present a general survey of our present knowledge in this field in different model organisms, protozoa, plants, yeast, and mammals. Questions still under debate and major challenges are discussed. Mitochondria are involved in numerous human diseases. The targeting of macromolecule to mitochondria represents a promising way to fight mitochondrial disorders and recent developments in this area of research are presented.
Subject(s)
RNA, Fungal/metabolism , RNA, Plant/metabolism , RNA, Protozoan/metabolism , RNA, Transfer/metabolism , RNA/metabolism , Animals , Base Sequence , Biological Evolution , DNA/metabolism , Humans , Mitochondrial Proteins/genetics , Mitochondrial Proteins/metabolism , Molecular Sequence Data , Nucleic Acid Conformation , RNA, Fungal/genetics , RNA, Mitochondrial , RNA, Plant/genetics , RNA, Protozoan/genetics , RNA, Ribosomal/genetics , RNA, Ribosomal/metabolism , RNA, Transfer/chemistry , RNA, Transfer/genetics , Ribonuclease P/genetics , Ribonuclease P/metabolismABSTRACT
All tRNA(His) possess an essential extra G(-1) guanosine residue at their 5' end. In eukaryotes after standard processing by RNase P, G(-1) is added by a tRNA(His) guanylyl transferase. In prokaryotes, G(-1) is genome-encoded and retained during maturation. In plant mitochondria, although trnH genes possess a G(-1) we find here that both maturation pathways can be used. Indeed, tRNA(His) with or without a G(-1) are found in a plant mitochondrial tRNA fraction. Furthermore, a recombinant Arabidopsis mitochondrial RNase P can cleave tRNA(His) precursors at both positions G(+1) and G(-1). The G(-1) is essential for recognition by plant mitochondrial histidyl-tRNA synthetase. Whether, as shown in prokaryotes and eukaryotes, the presence of uncharged tRNA(His) without G(-1) has a function or not in plant mitochondrial gene regulation is an open question. We find that when a mutated version of a plant mitochondrial trnH gene containing no encoded extra G is introduced and expressed into isolated potato mitochondria, mature tRNA(His) with a G(-1) are recovered. This shows that a previously unreported tRNA(His) guanylyltransferase activity is present in plant mitochondria.
