Effects of Cortisol-Protein Complexes on RNA Polymerase Activity in Isolated Pig Liver and Thymus Nuclei 1

Abstract

Summary

Cortisol is known to alter RNA polymerase activity in liver and thymus. It also binds to cytosol proteins in several tissues. These experiments tested the possibility that cytosol steroid-protein complexes could alter the RNA polymerase activity of homologous nuclei.

Steroid-protein complexes were prepared by incubating liver and thymus minces with 10^-7 M ³H-cortisol at 37°. The partially purified steroid-protein complexes were obtained by fractionation of the cytosol on Sephadex G-100. Steroid-protein complexes were incubated with intact homologous nuclei and a nuclear sediment was prepared by hypotonic lysis of nuclei and centrifugation. RNA polymerase activity was determined in the nuclear sediment.

It was found that a liver cytosol steroid-protein complex significantly (p < .01) increased RNA polymerase activity when compared to free cortisol or buffer. Cytosol proteins from adrenalectomized pigs had no effect on nuclear RNA polymerase. A steroid-protein complex in the thymus significantly decreased RNA polymerase activity in thymus nuclei when compared to buffer, but the difference was no greater than that observed for free cortisol. This indicates that an association of cortisol with liver cytosol proteins may be an early event in the action of cortisol.

This work was supported by a grant from the National Science Foundation (GB-29297). The authors appreciate the technical assistance of Mrs. Lois Jaques.