Plasmid-like DNA is part of mitochondrial DNA in Podospora anserina

Abstract

As previously reported, a ccc DNA with a contour length of 0.75 µm and molecular weight of 2.4 kb (termed plasmid-like, p1DNA) is the causative agent of senescence in the fungus Podospora anserina. Its postulated location in mtDNA was proved correct by the following experiments: 1. Restriction analysis of mtDNA resulted in different molecular weights for both, juvenile (95 kb) and senescent (30 kb) mtDNA. The construction of a detailed restriction map made evident the fact that senescent mtDNA comprises only a part of its juvenile counterpart. 2. Hybridization experiments (Southern blots) between (3)H-labelled plDNA and mtDNA cleaved by restriction juvenile mtDNA are homologous to plDNA. 3. Fine mapping experiments (construction of restriction maps and heteroduplex experiments) between plDNA integrated into a bacterial vector and its postulated equivalent, derived from juvenile mtDNA and also integrated into a bacterial vector, allowed a precise determination of the site of plDNA insertion within the juvenile mtDNA. All of these data fit into a previously published model in which, during aging, plDNA is excised from mtDNA and becomes autonomous for replication and function.