Evolutionary stability of mitochondrial DNA organization in Achlya

A physical map of the mtDNA (mitochondrial DNA) of Achlya klebsiana has been constructed. The molecule is circular and has a size of 50.7 ± 1.3 kilobases (kb). A large portion of genome exists in the form of an inverted repeat region, each copy being from 9.74 to 10.92 kb in length. Part of the repeat region is homologous to the yeast mitochondrial 21S rRNA gene. Two isomers of the molecule are present owing to a flip–flop rearrangement of the unique regions. Since no restriction-site differences have been detected between the two repeat regions, it is likely that the inverted repeat condition promotes continual sequence conversion, thus preserving the evolutionary advantages of gene duplication. The physical map of A. klebsiana mtDNA was compared with that of Achlya ambisexualis E-87 and it was found that the inverted repeat regions, as well as a 7-kb unique region adjacent to one of the repeat regions, were highly conserved with respect to restriction-site spacing.