labelling-visualization-mitochondrial-genome-expression-products

Labelling and Visualization of Mitochondrial Genome Expression Products in Baker's Yeast <em>Saccharomyces cerevisiae</em>

Mitochondria are essential organelles of eukaryotic cells capable of aerobic respiration. They contain circular genome and gene expression apparatus. A ...

M.V. Lomonosov Moscow State University

HU is a most abundant DNA-binding protein in bacteria. This protein is conserved either in its heterodimeric form or in one of its homodimeric forms in all bacteria, in plant chloroplasts, and in some viruses. HU protein non-specifically binds and bends DNA as a hetero- or homodimer and can participate in DNA supercoiling and DNA condensation. It also takes part in some DNA functions such as replication, recombination, and repair. HU does not recognize any specific sequences but shows some specificity to cruciform DNA and to repair intermediates, e.g., nick, gap, bulge, 3'-overhang, etc. To understand the features of HU binding to DNA and repair intermediates, a fast and easy HU proteins purification procedure is required. Here we report overproduction and purification of the HU homodimers. The method of HU purification allows obtaining a pure recombinant non-tagged protein cloned in Escherichia coli. We applied this method for purification of Acholeplasma laidlawii HU and demonstrated that this protein possesses a DNA-binding activity and is free of contaminating nuclease activity. Besides that we have shown that expression of A. laidlawii ihf_hu gene in a slow-growing hupAB E. coli strain restores the wild-type growth indicating that aclHU can perform the basic functions of E. coli HU in vivo.

Purification and functional analysis of recombinant Acholeplasma laidlawii histone-like HU protein.

Mitochondrial DNA is susceptible to the action of reactive oxygen species generated by the reactions of oxidative phosphorylation. Homologous recombination is one of the mechanisms providing integrity of the mitochondrial genome. Some proteins that take part in this process in budding yeast mitochondria have been identified. These include Abf2p, the major protein of the mt-nucleoid that specifically binds cruciform DNA, and Cce1p - Holliday junction resolvase. Here we show that Abf2p does not significantly affect either binding of Cce1p to branched DNA or rate and specificity of Holliday junction resolution. These data suggest the existence of an alternative homologous recombination pathway in yeast mitochondria.

Interaction between Saccharomyces cerevisiae Mitochondrial DNA-Binding Protein Abf2p and Cce1p Resolvase.

Protein biosynthesis in mitochondria is organized in a bacterial manner. However, during evolution, mitochondrial translation mechanisms underwent many organelle-specific changes. In particular, almost all mitochondrial translation factors, being orthologous to bacterial proteins, are characterized by some unique elements of primary or secondary structure. In the case of the organellar initiation factor 3 (IF3), these elements are several dozen amino acids long N- and C-terminal extensions. This study focused on the terminal extensions of baker's yeast mitochondrial IF3, Aim23p. By in vivo deletion and complementation analysis, we show that at least one extension is necessary for Aim23p function. At the same time, human mitochondrial IF3 is fully functional in yeast mitochondria even without both terminal extensions. While  IF3 itself is poorly active in yeast mitochondria, adding Aim23p terminal extensions makes the resulting chimeric protein as functional as the cognate factor. Our results show that the terminal extensions of IF3 have evolved as the "adaptors" that accommodate the translation factor of bacterial origin to the evolutionary changed protein biosynthesis system in mitochondria.

Biological and Evolutionary Significance of Terminal Extensions of Mitochondrial Translation Initiation Factor 3.

After billions of years of evolution, mitochondrion retains its own genome, which gets expressed in mitochondrial matrix. Mitochondrial translation machinery rather differs from modern bacterial and eukaryotic cytosolic systems. Any disturbance in mitochondrial translation drastically impairs mitochondrial function. In budding yeast , deletion of the gene coding for mitochondrial translation initiation factor 3 - , leads to an imbalance in mitochondrial protein synthesis and significantly delays growth after shifting from fermentable to non-fermentable carbon sources. Molecular mechanism underlying this adaptation to respiratory growth was unknown. Here, we demonstrate that slow adaptation from glycolysis to respiration in the absence of Aim23p is accompanied by a gradual increase of cytochrome c oxidase activity and by increased levels of Tma19p protein, which protects mitochondria from oxidative stress.

Article	Year
Purification and functional analysis of recombinant Acholeplasma laidlawii histone-like HU protein. Biochimie\| PubMed ID: 21443922	2011
Interaction between Saccharomyces cerevisiae Mitochondrial DNA-Binding Protein Abf2p and Cce1p Resolvase. Biochemistry. Biokhimiia\| PubMed ID: 27908236	2016
Biological and Evolutionary Significance of Terminal Extensions of Mitochondrial Translation Initiation Factor 3. International journal of molecular sciences\| PubMed ID: 30518034	2018
Strain Lacking Mitochondrial IF3 Shows Increased Levels of Tma19p during Adaptation to Respiratory Growth. Cells\| PubMed ID: 31248014	2019

Sergei A. Levitskii

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