Mitochondria are organelles that have their own genomic DNA. We are interested in the mechanisms by which the mitochondrial genome is propagated during the cell cycle. We try to understand what changes in the structure of DNA molecules take place during synthesis and how mitochondrial DNA replication and recombination are related. We are also interested in enzymes involved in mitochondrial DNA metabolism - DNA polymerase, which synthesizes mitochondrial DNA; nucleases required for DNA stability and helicases, which are motor enzymes that modulate the structure of nucleic acids.
Analysis of mitochondrial DNA topology and stable inheritance
Analysis by our group has shown that mitochondrial DNA forms complex higher-order network structures in yeast and cannot be described by the simple ring structures depicted in the textbooks. Our data indicate that such DNA structures are likely to result from recombination and that yeast mitochondria do not have the specific DNA synthesis initiation structures that should be present when using RNA primers.
The S. cerevisiae model organism allows us to systematically analyze the effects of various enzymes on mitochondrial DNA stability, as baker's yeast can grow without a functional respiratory chain. We have constructed yeast strains in which RNA synthesis in mitochondria is eliminated, allowing the identification of factors important in recombinant DNA synthesis.
Function of mitochondrial DNA helicases
As a rule, the DNA helicase is involved in DNA replication in various systems, and its task is to unravel the strands at the replication fork. As a result of our laboratory work, two DNA helicases have been identified in the mitochondria, but it has also been found that the classical replicative helicase in yeast mitochondria is apparently absent. For functional analysis of mitochondrial DNA helicases, we use a combination of biochemical experiments with purified proteins and in vivo analysis. Thus, we have shown that these mirochondrial helicases have specificity for branched-chain DNA molecules, suggesting their role in recombinant processes.
1. Piljukov VJ, Garber N, Sedman T, Sedman J.(2020) Irc3 is a monomeric DNA branch point-binding helicase in mitochondria of the yeast Saccharomyces cerevisiae. FEBS Lett. 594(19):3142-3155.
2. Sedman T, Garber N, Gaidutšik I, Sillamaa S, Paats J, Piljukov VJ, Sedman J. (2017) Mitochondrial helicase Irc3 translocates along double-stranded DNA. FEBS Lett. 591(23):3831-3841.
3. Wanrooij PH, Engqvist MKM, Forslund JME, Navarrete C, Nilsson AK, Sedman J, Wanrooij S, Clausen AR, Chabes (2017) Ribonucleotides incorporated by the yeast mitochondrial DNA polymerase are not repaired. Proc Natl Acad Sci U S A. ;114(47):12466-12471.
4. Gaidutšik I, Sedman T, Sillamaa S, Sedman J (2016) Irc3 is a mitochondrial DNA branch migration enzyme. Sci Rep. 6:26414.
5. Sedman T, Gaidutšik I, Villemson K, Hou Y, Sedman J. (2014) Double-stranded DNA-dependent ATPase Irc3p is directly involved in mitochondrial genome maintenance. Nucleic Acids Res. 42(21):13214-27.