Nuclear Poly(A) Polymerase Activities in the Rabbit Uterus

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Abstract
Poly(A) polymerase activities were measured from intact rabbit uterine nuclei and chromatin after a single dose of progesterone, and following a 5‐day treatment with progesterone alone or in combination with estradiol. A single intravenous dose of progesterone (5 mg/kg) to estrogen‐primed rabbits elicited an early increase in both bound and free nuclear poly(A) polymerase activities, the peak activity (about 40% over the controls) being reached 30–60 min posttreatment. The bound enzyme activity seemed to exhibit a second rise that occurred 12 h after progesterone administration. A 5‐day treatment of estrous rabbits with progesterone (1 mg/kg) brought about a sixfold elevation in the bound poly(A) polymerase and a twofold increase in the free nucleoplasmic enzyme activity. A corresponding activation also occurred in the chromatin‐associated poly(A) polymerase. Concomitant administration of estradiol (50 μg/kg) with progesterone significantly depressed progesterone‐elicited increases in the poly(A) polymerases. Changes in the nuclear RNA polymerase I and II were minor during a long‐term progesterone treatment, while the total chromatin template activity, as measured in a transcription system in vitro using wheat germ RNA polymerase II, was significantly reduced after a 5‐day progesterone administration. When estradiol was given along with progesterone, it counteracted the effect of progesterone on the chromatin template.These results suggest that progesterone exerts in the rabbit uterus posttranscriptional actions on the metabolism and processing of mRNA species. Moreover, the antiprogestational action of estrogens was already noted in the regulation of enzymes responsible for completion of mature mRNA synthesis.