The synthesis of DNA associated with the nuclear membrane of guinea pig adrenal cells

Abstract

Adrenal glands isolated from adrenocorticotropic hormone (ACTH)-treated animals and incubated in vitro in the presence of [ Me- 3H]thymidine were able to synthesize DNA. Nuclear isolation and fractionation after exposure of the glands to radioactive thymidine yielded particulate-bound DNA with a specific activity higher than that of total nuclear DNA. When pulse exposure was followed by further incubation in the presence of unlabelled thymidine, the radioactivity remained associated with the nuclear fraction sedimenting at a sucrose density of 1.22 (Fraction V) while a nuclear fraction sedimenting at a sucrose density of 1.09 (Fraction II) exhibited a decrease in its radioactive content followed by an increase and a second decay. DNA was purified from all the nuclear fractions obtained and its molecular weight was determined by continuous sucrose gradient. DNA polymerase (DNA nucleotidyltransferase, EC 2.7.7.7) activity was found to be associated with the fractions of intermediate densities when they were prepared from nuclei isolated from ACTH-stimulated adrenal glands, but not when they were prepared from nuclei isolated from unstimulated glands.