title: Biochemical aspects of cardiac muscle differentiation. Deoxyribonucleic acid synthesis and nuclear and cytoplasmic deoxyribonucleic acid polymerase activity.
abstract: DNA synthesis and DNA polymerase activity have been measured in terminally differentiating cardiac muscle of the rat. Incorporation of [3H]thymidine into DNA essentially ceases by the 17th day of postnatal development. Cardiac muscle of neonatal rats contains at least two molecular species of DNA polymerase: a 3.5 S DNA polymerase that can be extracted from nuclei with 0.2 m potassium phosphate and a 6 to 8 S soluble cytoplasmic DNA polymerase. The nuclear DNA polymerase in crude extracts has a pH optimum of 9.0 and is more active with native DNA than with denatured DNA as the primer-template. The cytoplasmic DNA polymerase in crude extracts has a pH optimum of 7.5 and is more active with denatured DNA. The activity of the 6 to 8 S cytoplasmic DNA polymerase decreases 80-fold from day 1 to day 17 after birth, which correlates temporally with the reduced rate of DNA synthesis. The activity of the 3.5 S nuclear DNA polymerase remains relatively constant throughout postnatal development. Mixing experiments (assay of neonatal enzyme extracts with adult enzyme extracts) gave additive results, suggesting that the decline in 6 to 8 S DNA polymerase activity apparently is not due to the presence of absence of soluble activators or inhibitors at different times during development. These studies may provide a system which can be used to investigate the control of DNA synthesis and cellular proliferation during the terminal stages of cardiac muscle differentiation.
mesh_terms: D000375:Aging; D000818:Animals; D000831:Animals, Newborn; D002454:Cell Differentiation; D002467:Cell Nucleus / Q000201:enzymology*; D003593:Cytoplasm / Q000201:enzymology*; D004254:DNA Nucleotidyltransferases / Q000378:metabolism*; D004261:DNA Replication; D006863:Hydrogen-Ion Concentration; D008970:Molecular Weight; D009206:Myocardium / Q000378:metabolism*; D009691:Nucleic Acid Denaturation; D051381:Rats; D013698:Templates, Genetic; D013936:Thymidine / Q000378:metabolism
chemical_list: D004254:DNA Nucleotidyltransferases; D013936:Thymidine