Abstract
Summary
Glucocorticoids are known to bind to liver cytosol proteins and alter nuclear RNA synthesis. Nuclear proteins are believed to assist in the regulation of nuclear RNA synthesis. The work reported here tested the possibilities that one of the very early effects of corticosterone treatment in rats consists of altered phosphorylation of nuclear proteins and that cytosol steroid-receptor complexes are necessary for altered phosphorylation of nuclear proteins.
It was found that phosphorylation of proteins in liver nuclei isolated from rats previously injected with corticosterone was significantly (p < 0.05) greater than control. Corticosterone in vitro had no effect when incubated directly with nuclei, but phosphorylation was significantly (p < 0.05) increased in nuclei previously incubated with rat liver cytosol containing 10−7 M corticosterone.
Corticosterone treatment increased phosphorylation in histones and nuclear acidic proteins. Although phosphorylation of histones was generally increased, no selective phosphorylation of any specific histone fraction was observed. In contrast, corticosterone administration resulted in a significant selective increase in the phosphorylation of a nuclear acidic protein fraction.
This work was supported by ACS BC-37 and NSF GB-29297 grants. The authors appreciate the technical assistance of Curt Lundgren and Rosemary Jonassen.
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