The in vitro interaction of the carcinogens, 4-nitroquinoline-N-oxide and its metabolite 4-hydroxylaminoquinoline-N-oxide, with intact rat liver mitochondria

Comment: mitochondrial genes and cancer

As a result of an experimental confluence between carcinogenesis and oxidative phosphorylation, we published in 1971 'A Unitary Hypothesis for Carcinogenesis' [(1971) J. Antibiot. Tokyo 24, 405-417]. According to this hypothesis, damaged mitochondria release mitochondrial genetic material which like that from an oncogenic virus could enter the nuclear genome. Our original hypothesis and its justification cover the hypothesis recently presented by Dr C. Richter [(1988) FEBS Lett. 241, 1-5].

Mitochondrial DNA and nuclear DNA from normal rat liver have a common sequence

Although Pst I does not cut the circular mitochondrial genome of the rat, BamHI generates from this genome two unequal fragments of DNA. Each of these fragments was cloned in pBR322. Nuclear DNA was digested from rat liver singly or doubly with Pst I and BamHI, and it was demonstrated that nuclear DNA shared a common sequence with the larger mitochondrial DNA BamHI fragment. The cloned larger mitochondrial DNA fragment was further subdivided with HindIII into four pieces that were labeled and then used to probe the double-digested nuclear DNA. The hybridization data showed that the common sequence is less than 3 kilobase pairs long and lies within the part of the mitochondrial genome containing the D-loop and a portion of the rRNA genes. It therefore appears that, as in lower eukaryotes, there are shared sequences between the nuclear and mitochondrial genomes in mammals.