Early changes in nucleoplasmic poly(A) polymerase activity in immature rabbit uterus after estradiol administration

To study the role of post-transcriptional polyadenylation in the mechanism of estrogen action, we measured free nucleoplasmic poly(A) polymerase activity in intact uterine nuclei of immature rabbits at timed intervals after a single intravenous dose of estradiol (20 microgram/kg body weight). Uterine nuclear poly(A) polymerase activity was altered in a biphasic manner by estradiol treatment with maximal activities occurring at 0.5 h and 12 h of steroid administration, at which time periods they were about 2- and 3-fold higher than pretreatment levels, respectively. The later increase in the enzyme activity was totally abolished by a prior cycloheximide (0.5 mg/kg) administration, whereas the initial activation of poly(A) polymerase seemed to occur via mechanism(s) independent of protein synthesis. It thus appears that changes in uterine nuclear poly(A) polymerase closely resemble those previously reported for the activity of RNA polymerase II after estradiol treatment.