Inversions and recombinations in mitochondrial DNA of the (SG-1) cytoplasmic mutant in two Neurospora species

Summary The mitochondrial DNAs of SG-1] cytoplasmically-mutant and wild-type strains of Neurospora crassa and Neurospora sitophila were examined by comparative restriction endonuclease analyses. The mtDNA of N. sitophila wild type of Whitehouse differs from type II mtDNA of N. crassa by insertions of 3.3 kb in EcoRI-9, and 1.2 kb in EcoRI-3, and a deletion of 1.1 kb in EcoRI-5. These DNA heteromorphisms provided convenient markers for tracing N. crassa SG-1] mtDNA during and after its transfer into N. sitophila. The SG-1] cytoplasmic mutant in both N. crassa and N. sitophila has a distinctive inversion that connects the fragment EcoRI-4 with HindIII-10a. The SG-1] mtDNA from N. crassa remained essentially intact after it was transferred by crosses into N. sitophila. In each species, a unique second inversion occured in the SG-1] mtDNA after the transfer was made. In N. sitophila, polar recombination in heteroplasmons between SG-1] and wild-type preferentially yields strains with mtDNAs that contain the maximum possible number of insertions in the cob and co-1 loci of the EcoRI-3 region of the mitochondrial chromosome.