Multiple Forms of DNA-Dependent RNA Polymerase I from Immature Chick Liver. Selective Effect of 17beta-Estradiol

Abstract

A single injection of 17.beta.-estradiol into immature chicks resulted within 24 h in a 2-fold increase of the transcriptional capacity of liver nuclei which involved both endogenous RNA polymerase I and II activities. RNA polymerase activity I of purified nucleoli was also doubled. During purification of RNA polymerase I from controls and treated chicks the difference in activity was almost completely lost. RNA polymerase I could be resolved into 2 forms, IA and IB, on CM-Sephadex. Form IA increased and form IB decreased after estrogen treatment, while the sum of the 2 remained constant. Form IA sedimented more slowly than form IB in glycerol gradients and was predominant in purified nucleoli. There may be an equilibrium between the 2 forms of RNA polymerase I which may change in order to produce the translational shift-up which occurs after estrogen treatment.