DNA Recombination-Initiation Plays a Role in the Extremely Biased Inheritance of Yeast [rho⁻] Mitochondrial DNA That Contains the Replication Origin ori5

Abstract

Hypersuppressiveness, as observed inEukaryotic cells gain most of the energy required for cellular functions by oxidative respiration in mitochondria. These organelles contain hundreds to thousands of copies of a mitochondrial DNA (mtDNA) genome that encodes components essential for respiration and protein synthesis. Generally, mitochondrial alleles segregate during vegetative cell growth (vegetative segregation), and all copies of mtDNA within a cell or an individual generally have the same sequence (homoplasmy). In patients with mitochondrial myopathies, the progressive accumulation of mtDNA with large deletions leads to a heteroplasmic state in specific tissues (20; for review, see references 43 and 54). This phenomenon may be caused by the selective replication and/or segregation of mtDNA bearing the deletion; however, genetic analysis of mtDNA processes in mammals has been hampered by the strict maternal inheritance of mitochondria. The yeast Saccharomyces cerevisiae is a suitable model system because of its biparental mtDNA inheritance (14).The extremely biased inheritance of mtDNA with a large deletion is known in S. cerevisiae as "hypersuppressiveness. Two mechanisms for the initiation of mtDNA replication in yeast have been proposed: mitochondrial transcriptional RNA polymerase (Rpo41)-primed initiation and recombination-mediated initiation. Rpo41-primed DNA replication is similar to that observed in mammalian mitochondria. In support of this mechanism, each mtDNA replication origin shares sequence similarity with the heavy-strand replication origin of mammalian mtDNA, including the presence of a transcription promoter and three GC-rich clusters (2, 13). RNA synthesized by Rpo41 from mtDNA replication-origin promoters has been detected, and an endoribonuclease that cleaves the synthesized RNA at sites that correspond to regions of transition from RNA to DNA synthesis has been detected (3,49,53). The intact replication-origin promoter is required for hypersuppressiveness (36). However, this transcription-dependent process is not the sole mechanism for the initiation of mtDNA replication, since both the replication origin and RPO41 are dispensable for the maintenance of [rho Ϫ ] mtDNA (18,53). In addition, it has been reported that the selective inheritance of hypersuppressive [rho Ϫ ] mtDNA relative to nonhypersuppres-* Corresponding author. Mailing address:

Mechanism of Homologous Recombination and Implications for Aging-Related Deletions in Mitochondrial DNA

“…Mutation in MHR1 reduces concatemer formation, which subsequently affects the partitioning of newly synthesized mtDNA into the buds and delays the establishment of mtDNA homoplasmy in the daughter cells (200,201). Mhr1 is also required for the replicative advantage of the ori5 hypersuppressive Ϫ genome, which has apparently frequent double-strand breaks (202), consistent with its role in recombinational repair of mtDNA. It was initially proposed that Mhr1 may have a Rad52-type activity like Red␤ in the phage .…”

Novel subfamily of mitochondrial HMG box-containing proteins: functional analysis of Gcf1p from Candida albicans

“…The severe reduction of Gcf1p levels in C. albicans mitochondria under repressed conditions apparently leads to the observed decrease in recombination structures that could be used for initiation of mtDNA replication. Recently, it has been demonstrated that in yeast recombination is linked to the initiation of mtDNA replication (Ling et al, 2007;J. M. Gerhold and others, unpublished results).…”

Replication Intermediates of the Linear Mitochondrial DNA of Candida parapsilosis Suggest a Common Recombination Based Mechanism for Yeast Mitochondria

“…5). We and others have previously discussed the universal impact of RDR in organelle DNA maintenance with examples from yeasts, plants, and human heart (7,(51)(52)(53)(54)(55)(56). A link between topology and maintenance mechanisms has been drawn for chloroplast DNA (54), and this concept applies for C. albicans mtDNA as well.…”