Irc3 is a mitochondrial DNA branch migration enzyme

Ilja Gaidutšik,Juhan Sedman,Tiina Sedman,Sirelin Sillamaa

doi:10.1038/srep26414

Abstract

Integrity of mitochondrial DNA (mtDNA) is essential for cellular energy metabolism. In the budding yeast Saccharomyces cerevisiae, a large number of nuclear genes influence the stability of mitochondrial genome; however, most corresponding gene products act indirectly and the actual molecular mechanisms of mtDNA inheritance remain poorly characterized. Recently, we found that a Superfamily II helicase Irc3 is required for the maintenance of mitochondrial genome integrity. Here we show that Irc3 is a mitochondrial DNA branch migration enzyme. Irc3 modulates mtDNA metabolic intermediates by preferential binding and unwinding Holliday junctions and replication fork structures. Furthermore, we demonstrate that the loss of Irc3 can be complemented with mitochondrially targeted RecG of Escherichia coli. We suggest that Irc3 could support the stability of mtDNA by stimulating fork regression and branch migration or by inhibiting the formation of irregular branched molecules.

Highlights

IntroductionIntegrity of mitochondrial DNA (mtDNA) is essential for cellular energy metabolism. In the budding yeast Saccharomyces cerevisiae, a large number of nuclear genes influence the stability of mitochondrial genome; most corresponding gene products act indirectly and the actual molecular mechanisms of mtDNA inheritance remain poorly characterized
Integrity of mitochondrial DNA is essential for cellular energy metabolism
Distinctive Y and X arcs usually interpreted as replication forks and Holliday junctions, respectively, were readily detected in a11 mitochondrial DNA (mtDNA) preparations (Y and X, Fig. 1c, wt)

Summary

Introduction

Integrity of mitochondrial DNA (mtDNA) is essential for cellular energy metabolism. In the budding yeast Saccharomyces cerevisiae, a large number of nuclear genes influence the stability of mitochondrial genome; most corresponding gene products act indirectly and the actual molecular mechanisms of mtDNA inheritance remain poorly characterized. While recombination appears to play an important role in yeast mtDNA metabolism, little is known about the protein factors including DNA helicases involved in the formation and processing of branched recombination intermediates. Two DNA helicases of the Superfamily I - Pif[1] and Hmi1 - have been identified in yeast mitochondria[19,20] and both enzymes have been suggested to play a role in recombination. Branch migration helicases that are important for a variety of recombination-related processes, including recombinational DNA repair, recovery of stalled replication forks and suppression of ectopic recombination, have not been described in yeast mitochondria, where the levels of three- and four-way junctions in DNA are high. Prokaryotic branch migration helicases- and none of the yeast nuclear branch migration enzymes has been shown to be targeted to mitochondria

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