Search for mitochondrial DNA sequences in chick nuclear DNA

Abstract

1. We have carried out hybridization experiments, using a standard nitrocellulose filter assay, to ascertain whether mtDNA sequences are present in nuclear DNA. Nuclear DNA was isolated from purified chick erythrocyte nuclei, to minimize contamination with mtDNA. Mitochondrial DNA sequences in nuclear DNA were detected by hybridization with complementary RNA of high specific radioactivity, synthesized on highly purified mtDNA with RNA polymerase of Escherichia coli. The hybridization to be expected for one copy of mtDNA per haploid nucleus was determined with known mixtures of nuclear DNA and 2–16 copies of mtDNA. This value was corrected for non-specific adsorption to rat nuclear DNA. 2. The hybridization found corresponds to 1–3 mtDNA copies per haploid nucleus. This value was confirmed by a semi-quantitative kinetic method in which the rate of conversion of complementary RNA into a ribonuclease-resistant form is determined in the presence of known amounts of nuclear and mtDNA. 3. Although our results could be attributable to the presence of 1–3 mtDNA “master copies” per haploid nuclear DNA, contamination of the nuclear DNA preparations by this amount of mtDNA explains the results equally well.