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Characterization of two new plasmid DNAs found in mitochondria of wild-type Neurospora intermedia strains
Abstract:
Mitochondria from two Neurospora intermedia strains (P4O5-Labelle and Fiji N6-6) were found to contain plasmid DNAs in addition to the standard mitochondrial DNA species. The plasmid DNAs consist of monomeric circles (4.1-4.3 kbp and 5.2-5.3 kbp for Labelle and Fiji, respectively) and oligomers in which monomers are organized as head-to-tail repeats. DNA-DNA hybridization experiments showed that the plasmids have no substantial sequence homology to mtDNA, to each other, or to a previously characterized mitochondrial plasmid from N. crassa strain Mauriceville-lc (Collins et al. Cell 24, 443-452, 1981). The intramitochondrial location of the plasmids was established by cell fractionation and nuclease protection experiments. In sexual crosses, the plasmids showed strict maternal inheritance, the same as Neurospora mitochondrial DNA. The plasmids may represent a novel class of mitochondrial genetic elements.
Insights
Novel plasmid DNAs were discovered within the mitochondria of two Neurospora intermedia strains. These mitochondrial plasmids, distinct from known DNA, exhibit maternal inheritance, suggesting a new class of genetic elements.
Area of Science:
- Mitochondrial genetics
- Molecular biology
- Fungal genomics
Background:
- Mitochondria contain their own genetic material, mitochondrial DNA (mtDNA).
- Extrachromosomal DNA elements can exist within mitochondria, influencing cellular functions.
- Neurospora intermedia is a model organism for studying fungal mitochondrial genetics.
Purpose of the Study:
- To investigate the presence and characteristics of extrachromosomal DNA in Neurospora intermedia mitochondria.
- To determine the relationship of these DNA elements to the standard mitochondrial genome and other known plasmids.
- To understand the inheritance pattern of these novel mitochondrial DNA elements.
Main Methods:
- Isolation and characterization of plasmid DNA from Neurospora intermedia strains.
- DNA-DNA hybridization to assess sequence homology.
- Cell fractionation and nuclease protection assays to confirm intramitochondrial localization.
- Analysis of inheritance patterns through sexual crosses.
Main Results:
- Two Neurospora intermedia strains harbor unique mitochondrial plasmid DNAs (4.1-5.3 kbp) alongside mtDNA.
- These plasmids show no significant sequence homology to mtDNA, to each other, or to the N. crassa Mauriceville-lc plasmid.
- Plasmids are located within mitochondria and exhibit strict maternal inheritance, similar to mtDNA.
- Plasmids exist as monomers and head-to-tail oligomers.
Conclusions:
- Mitochondria of Neurospora intermedia harbor a novel class of plasmid DNA.
- These plasmids represent a distinct genetic entity within the fungal mitochondrion.
- The findings expand our understanding of mitochondrial genetic diversity and organization in eukaryotes.