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SUMMARY
DNA polymerase activity was found in the cytoplasmic fraction and in isolated nuclei from anterior pituitary glands of male rats. The enzyme activity was assayed by measuring the incorporation of [3H]dTTP into DNA in a medium containing Tris-HCl buffer (pH 8·5), the four deoxyribonucleoside triphosphates, Mg2 +, ATP and activated calf thymus DNA. The DNA polymerase activity decreased with age in glands from animals aged 25 days to over a year but increased after oestrone treatment in vivo. These changes in activity, more pronounced in the cytoplasmic fraction than in the isolated nuclei, were similar to changes in DNA synthesis measured in anterior pituitary glands under the same physiological conditions.
Isolated nuclei also retained endogenous DNA synthetic activity in the absence of added template. Addition of a cytoplasmic fraction to the reaction medium stimulated activity by as much as 1·9-fold but the degree of stimulation was the same whether the cytoplasm was from young, old or oestrone-treated animals.
