Molecular characterization of the mitochondrial DNA of a new stopper mutant ER-3 of Neurospora crassa.

An ethidium bromide-induced stopper mutant of Neurospora crassa is characterized at the molecular level. The mutant has two populations of mitochondrial DNA: a defective predominant mutant molecule and a basal level of the wild-type molecule. The aberrant DNA resulted after a 25-kbp deletion from the wild-type mitochondrial chromosome, which included major genes such as cytb, co1 and oli2. The deletion endpoints are located in the second intron of the ND5 gene, and in a sequence 250 nucleotides upstream of the co2 gene. The recombination has taken place between two nine nucleotide repeats CCCCGCCCC, one of which is close to a PstI palindrome at its 5' end. Thus the mutant ER-3 differs from all the other stopper mutants described previously in the extent and location of the deletions in the mtDNA.