PHYSICAL AND GENETIC-MAP OF THE MITOCHONDRIAL GENOME OF CRYPHONECTRIA-PARASITICA EP155

In the chestnut-blight fungus, Cryphonectria parasitica, a cytoplasmic ally transmissible (infectious) form of hypovirulence is associated wi th mitochondrial DNA (mtDNA) mutations that cause respiratory deficien cies. To facilitate the characterization of such mutations, a restrict ion map including the probable location of 13 genes was constructed fo r a relatively well-characterized virulent strain of the fungus, Ep155 . The physical map is based on the order of all fragments generated by cleavage of the mtDNA by the PstI restriction endonuclease and includ es some of the cleavage sites for HindIII, EcoRI, and XbaI. It was con structed from hybridization patterns of cloned mtDNA fragments with So uthern blots of mtDNA digested with the four restriction enzymes. On t his map, the probable locations of genes commonly found in the mitocho ndrial genomes of ascomycetes were determined by low-stringency hybrid ization of cloned Neurospora crassa mitochondrial gene probes to South ern blots of C. parasitica mtDNA. The data indicate that the mtDNA of strain Ep155 is a circular molecule of approximately 157 kbp and ranks among the largest mitochondrial chromosomes observed so far in fungi. The mtDNAs of 11 different C. parasitica isolates range in size from 135 to 157 kbp and in relatedness from 68 to 100 percent, as estimated from restriction-fragment polymorphisms. In addition to the typical m tDNA, the mitochondria of some isolates of the fungus contain double-s tranded DNA plasmids consisting of nucleotide sequences not represente d in the mtDNA of Ep155.