Microheterogeneity detected in circular dimer mitochondrial DNA

Exhaustive EcoRI digests of circular dimer mitochondrial DNA (mtDNA) from mouse cell lines LD and LDTK- yield two major fragments whose average lengths are slightly smaller than the corresponding fragments of circular monomer mtDNA from mouse LA9 and LMTK- cells. A third fragment approximately 400 nucleotide pairs in length is frequently produced in less than molar yield. Exhaustive EcoRI digests of circular dimer mtDNA from human acute myelogenous leukemic leucocytes yield three major fragments. The presence of mtDNA resistant to cleavage as well as fragments of intermediate sizes indicatesmicroheterogeneity in the genomic positions of EcoRI recognition sequences in both mouse and human circular dimer mtDNA. Analysis of the distribution averages of circular contour lengths indicates microheterogeneity in the sizes of mouse LD and human mtDNAs. The denatured-renatured EcoRI fragments frequently contain a small loop(s) of single-strand DNA as would occur for deletion(s) or addition(s) of nucleotide sequences in some of the circular dimer molecules.