Effect of estrogen on the elongation rate and number of RNA chains being synthesized in uterine nucleoli.

Administration of estradiol (E2) to ovariectomized mature rats resulted in a time-dependent increased transcriptional activity of uterine nucleoli isolated from hormone-treated animals compared to uterine nucleoli isolated from control animals. Early (4 h) E2 stimulation of uterine nucleolar transcription, resulted from an increased rate of elongation of chain growth on preinitiated nucleolar RNA with no significant effect of E2 on the number of nucleolar RNA chains being synthesized. Longer (24 h) treatment of animals with hormone resulted in both significant increased numbers of uterine nucleolar RNA chains in the act of synthesis and increased rate of elongation of nucleolar RNA chain growth. Salt extraction (150 mM NaCl) of uterine nucleoli isolated from 4 h E2-treated animals decreased transcriptional activity to the level observed in nucleoli isolated from control animals. The loss in nucleolar transcriptional activity from salt extraction was due to decreased rate of elongation of nucleolar RNA synthesis with no significant effect on the number of RNA chains being synthesized. Salt extracts from nucleoli isolated from 4 h E2-treated animals, but not control animals, contained factor(s) capable of stimulating the rate of elongation of nucleoli isolated from control animals to elongation rates observed in unextracted nucleoli isolated from 4 h E2-treated animals. Synthesis and phosphorylation of a high molecular weight uterine nucleolar protein(s) was seen after 4 h of E2 treatment with the nucleolar phosphoprotein(s) salt extractable.