Abstract
Tritiated 5-bromo-2′-deoxyuridine was used as a precursor for the synthesis in vivo of nuclear and mitochondrial deoxyribonucleic acid in rat liver. Radioactivity was incorporated into a band of mitochondrial DNA which had a higher buoyant density than previously existing unlabeled DNA. The difference in density between labeled and unlabeled mitochondrial DNA bands doubled if the DNA was denatured after the introduction of strand breakages to allow complete separation of complementary strands. The result suggests that replication of mitochondrial DNA is by a semiconservative mechanism and that there is little, if any, repair of the DNA. Similar results leading to the same conclusions were obtained for nuclear DNA.
Highlights
Tritiated 5-bromo-2’-deoxyuridiine was used as a precursor for the synthesis in vivo of nuclear and mitochondriai deoxyribonucleic acid in rat liver
BUDR increasesthe incorporation of the latter approximately Several questionsare raised by these results. (a) Does the 10 times
The probablemechanismof this action is by inhibirapid turnover of mitochondrialDNA representsynthesisof new tion of the biosynthesisof dTMP [3]. completestrandsof DNA or is it dueto repair and replacement The rats werefirst given 15 mg of 5-fluorouracil (RocheLabof segmentswithin existingstrandsof DNA? (b) If new strand oratories)in 0.2 ml of isotonic0.9% NaCl solutionby intrapersynthesisis responsiblefor the observedturnover of mitochon- itoneal injection
Summary
Tritiated 5-bromo-2’-deoxyuridiine was used as a precursor for the synthesis in vivo of nuclear and mitochondriai deoxyribonucleic acid in rat liver. Radioactivity was incorporated into a band of mitochondrial DNA which had a higher buoyant density than previously existing unlabeled DNA. The tierencein density between labeled and unlabeled mitochondrial DNA bands doubled if the DNA was denatured after the introduction of strand breakagesto allow completeseparation of complementary strands. The result suggests that replication of mitochondrial DNA is by a semiconservativemechanism and that there is little, if any, repair of the DNA. Similar results leading to the same conclusions were obtained for nuclear DNA
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